I am using https://github.com/SofusA/roslyn-language-server (which basically wraps the microsoft roslyn lsp server since sublime lsp doesn't support named pipes yet) for C# but there are no diagnostics. The reason seems to be that sublime doesn't request correct textDocument/diagnostic even after they are registered. I am attaching both the VSCode traces and sublime lsp logs below for comparison. Comparing the logs it can be seen that even though the DocumentCompilerSemantic was registered along with some other options, sublime doesn't request for them whereas VSCode does and it is this request that provides the diagnostics.

sublime-logs.txt
trace.txt