Unsupported OCaml version 4.10.0

[avegancafe]

A couple of days ago I was working on a project in vscode using this extension, and when I came back today I'm getting a message "Unsupported OCaml version 4.10.0", cannot save because I guess it's trying to access my ocaml version, and totally freezes the editor since it cannot get it. I haven't changed anything, but I only have one version of ocaml installed and it's 4.09.0, not even 4.10.0. Is this a known issue? Here is my logs that the template requested:

Logs...

Hello - from /Users/kyle/.vscode/extensions/jaredly.reason-vscode-1.7.8/bin.native
Previous log location: /var/folders/2_/yqrm0ztd7tq3wclxpk0mq2100000gp/T/lsp.log
Sending notification {"jsonrpc": "2.0", "method": "client/registerCapability", "params": {"registrations": [{"id": "watching", "method": "workspace/didChangeWatchedFiles", "registerOptions": {"watchers": [{"globPattern": "**/bsconfig.json"}, {"globPattern": "**/.merlin"}]}}]}}
Sending response {"id": 0, "jsonrpc": "2.0", "result": {"capabilities": {"textDocumentSync": 1, "hoverProvider": true, "completionProvider": {"resolveProvider": true, "triggerCharacters": ["."]}, "signatureHelpProvider": {"triggerCharacters": ["("]}, "definitionProvider": true, "typeDefinitionProvider": true, "referencesProvider": true, "documentSymbolProvider": true, "codeActionProvider": true, "executeCommandProvider": {"commands": ["reason-language-server.add_to_interface_inner"]}, "codeLensProvider": {"resolveProvider": true}, "documentHighlightProvider": true, "documentRangeFormattingProvider": true, "documentFormattingProvider": true, "renameProvider": true}}}
Read message 
{"jsonrpc":"2.0","method":"initialized","params":{}}
Read message 
{"jsonrpc":"2.0","method":"workspace/didChangeConfiguration","params":{"settings":{"reason_language_server":{"location":"","build_system_override_by_root":{},"refmt":"","lispRefmt":"","mlfmt":"","format_width":80,"per_value_codelens":false,"dependencies_codelens":true,"opens_codelens":true,"show_module_path_on_hover":true,"reloadOnChange":false,"show_debug_errors":true,"autoRebuild":true}}}}
Read message 
{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file:///Users/kyle/workspace/financial-analysis/Main.re","languageId":"reason","version":1,"text":"module Res = ReWeb.Response\n\n/* Define a service (i.e. function) to handle a \"hello\" GET request */\nlet hello = _ => \"Hello, World!\" |> Response.of_text |> Lwt.return;\n\n/* Define a service to handle requests that do not have a specified route */\nlet notFound = _ => `Not_found |> Response.of_status |> Lwt.return;\n\n/* Define routes via pattern matching; Note that we must be exhaustive */\nlet routes =\n  fun\n  | (`GET, [\"hello\"]) => hello\n  | _ => notFound;\n\n/* Run the server */\nlet () = Server.serve(routes);\n\n"}}}
Found a `dune` file at /Users/kyle/workspace/financial-analysis
]] Making a new jbuilder package at /Users/kyle/workspace/financial-analysis
=== Project root: /Users/kyle/workspace/financial-analysis
Detected `esy` dependency manager for local use
Get ocaml stdlib dirs
New dune process
[MerlinFile]: Error: Insufficient build files found for module AccessControlAllowOrigin - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/AccessControlAllowOrigin.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module StrictTransportSecurity - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module CacheControl - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Directive - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/Directive.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module ContentSecurityPolicy - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module SetCookie - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_fmt_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_fmt_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Main - src: /Users/kyle/workspace/financial-analysis/Main.re, srci: (), cmi: (), cmt: (), cmti: ()
>> Build system running: esy
>>> stdout

>>> stderr
info esy 0.6.4 (using package.json)
Affected files: 
Cleaning bsconfig.json
Sending notification {"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": {"uri": "file:///Users/kyle/workspace/financial-analysis/bsconfig.json", "diagnostics": []}}
Sending notification {"jsonrpc": "2.0", "method": "window/showMessage", "params": {"type": 1, "message": "Unsupported OCaml version: 4.10.0"}}
Found a `dune` file at /Users/kyle/workspace/financial-analysis
]] Making a new jbuilder package at /Users/kyle/workspace/financial-analysis
=== Project root: /Users/kyle/workspace/financial-analysis
Detected `esy` dependency manager for local use
Get ocaml stdlib dirs
New dune process
[MerlinFile]: Error: Insufficient build files found for module AccessControlAllowOrigin - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/AccessControlAllowOrigin.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module StrictTransportSecurity - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module CacheControl - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Directive - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/Directive.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module ContentSecurityPolicy - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module SetCookie - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_fmt_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_fmt_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Main - src: /Users/kyle/workspace/financial-analysis/Main.re, srci: (), cmi: (), cmt: (), cmti: ()
>> Build system running: esy
>>> stdout

>>> stderr
info esy 0.6.4 (using package.json)
Affected files: 
Cleaning bsconfig.json
Sending notification {"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": {"uri": "file:///Users/kyle/workspace/financial-analysis/bsconfig.json", "diagnostics": []}}
Read message 
{"jsonrpc":"2.0","id":1,"method":"textDocument/documentSymbol","params":{"textDocument":{"uri":"file:///Users/kyle/workspace/financial-analysis/Main.re"}}}
[server] Got a method textDocument/documentSymbol
[server] processing took 0.0109672546387ms
Found a `dune` file at /Users/kyle/workspace/financial-analysis
]] Making a new jbuilder package at /Users/kyle/workspace/financial-analysis
=== Project root: /Users/kyle/workspace/financial-analysis
Detected `esy` dependency manager for local use
Get ocaml stdlib dirs
New dune process
[MerlinFile]: Error: Insufficient build files found for module AccessControlAllowOrigin - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/AccessControlAllowOrigin.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module StrictTransportSecurity - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module CacheControl - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Directive - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/Directive.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module ContentSecurityPolicy - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module SetCookie - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_fmt_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_fmt_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Main - src: /Users/kyle/workspace/financial-analysis/Main.re, srci: (), cmi: (), cmt: (), cmti: ()
>> Build system running: esy
>>> stdout

>>> stderr
info esy 0.6.4 (using package.json)
Affected files: 
Cleaning bsconfig.json
Sending notification {"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": {"uri": "file:///Users/kyle/workspace/financial-analysis/bsconfig.json", "diagnostics": []}}
Sending response {"id": 1, "jsonrpc": "2.0", "error": {"code": -32603, "message": "Unsupported OCaml version: 4.10.0"}}
Read message 
{"jsonrpc":"2.0","method":"$/cancelRequest","params":{"id":1}}
Read message 
{"jsonrpc":"2.0","id":2,"method":"textDocument/documentSymbol","params":{"textDocument":{"uri":"file:///Users/kyle/workspace/financial-analysis/Main.re"}}}
[server] Got a method textDocument/documentSymbol
[server] processing took 0.00405311584473ms
Found a `dune` file at /Users/kyle/workspace/financial-analysis
]] Making a new jbuilder package at /Users/kyle/workspace/financial-analysis
=== Project root: /Users/kyle/workspace/financial-analysis
Detected `esy` dependency manager for local use
Get ocaml stdlib dirs
New dune process
[MerlinFile]: Error: Insufficient build files found for module AccessControlAllowOrigin - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/AccessControlAllowOrigin.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module StrictTransportSecurity - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module CacheControl - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Directive - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/Directive.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module ContentSecurityPolicy - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module SetCookie - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_fmt_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_fmt_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Main - src: /Users/kyle/workspace/financial-analysis/Main.re, srci: (), cmi: (), cmt: (), cmti: ()
>> Build system running: esy
>>> stdout

>>> stderr
info esy 0.6.4 (using package.json)
Affected files: 
Cleaning bsconfig.json
Sending notification {"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": {"uri": "file:///Users/kyle/workspace/financial-analysis/bsconfig.json", "diagnostics": []}}
Sending response {"id": 2, "jsonrpc": "2.0", "error": {"code": -32603, "message": "Unsupported OCaml version: 4.10.0"}}
Read message 
{"jsonrpc":"2.0","id":3,"method":"textDocument/codeLens","params":{"textDocument":{"uri":"file:///Users/kyle/workspace/financial-analysis/Main.re"}}}
[server] Got a method textDocument/codeLens
[server] processing took 0.00500679016113ms
Found a `dune` file at /Users/kyle/workspace/financial-analysis
]] Making a new jbuilder package at /Users/kyle/workspace/financial-analysis
=== Project root: /Users/kyle/workspace/financial-analysis
Detected `esy` dependency manager for local use
Get ocaml stdlib dirs
New dune process
[MerlinFile]: Error: Insufficient build files found for module AccessControlAllowOrigin - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/AccessControlAllowOrigin.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module StrictTransportSecurity - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/StrictTransportSecurity.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module CacheControl - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/CacheControl.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Directive - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/Directive.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module ContentSecurityPolicy - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/ContentSecurityPolicy.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module SetCookie - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.ml, srci: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__reweb-2d0d8e49/lib/re-web/ReWeb/Header/SetCookie.mli, cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Logs_fmt_top_init - src: /Users/kyle/.esy/3____________________________________________________________________/i/opam__s__logs-opam__c__0.7.0-ca5aee73/lib/logs/logs_fmt_top_init.ml, srci: (), cmi: (), cmt: (), cmti: ()
[MerlinFile]: Error: Insufficient build files found for module Main - src: /Users/kyle/workspace/financial-analysis/Main.re, srci: (), cmi: (), cmt: (), cmti: ()
>> Build system running: esy
>>> stdout

>>> stderr
info esy 0.6.4 (using package.json)
Affected files: 
Cleaning bsconfig.json
Sending notification {"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": {"uri": "file:///Users/kyle/workspace/financial-analysis/bsconfig.json", "diagnostics": []}}
Sending response {"id": 3, "jsonrpc": "2.0", "result": [{"range": {"start": {"line": 0, "character": 0}, "end": {"line": 0, "character": 0}}, "command": {"title": "Unable to load compilation data: Unsupported OCaml version: 4.10.0", "command": ""}}]}
Read message 
{"jsonrpc":"2.0","method":"$/cancelRequest","params":{"id":2}}

[enessoylu]

I am also getting errors for 4.09.0 and 4.10.0
It looks like extension is not supporting that versions yet (#317)

You can try switching your ocaml version:
opam switch create 4.08.0

[mrkaspa]

I have the same problem

[avegancafe]

Sorry just responding to this, @enessoylu I have the correct version of ocaml installed and used, I actually don't even have 4.10.0 installed which is the weird part

[avegancafe]

I also uninstalled this extension and installed OCaml and Reason IDE instead and everything seems to be working fine with that one, not sure if that helps give any more context at all

[vogler]

I actually don't even have 4.10.0 installed which is the weird part

Maybe a local switch (_opam directory)?

[chinwobble]

I'm also having this issue.

Would it be easy to update to ocaml 4.9 and ocaml 4.10?

I can see that the configuration is here.
https://github.com/jaredly/reason-language-server/blob/master/src/analyze/BuildSystem.re#L141

[mununki]

I guess this extension seems literally not supporting > v4.08.0 as @chinwobble pointed. So like @keyboard-clacker metioned above, I uninstalled this ext and install this (https://github.com/reasonml-editor/vscode-reasonml). It works now.