[Bug]: 4.0.1 Adding folders with many subfolders throws error

[bege10]

⚠️ Before submitting, please verify the following: ⚠️

• This is a bug, not a question or a configuration issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server and Desktop Client are up to date. See Server Maintenance and Release Schedule and Desktop Releases for supported versions.
• I agree to follow Nextcloud's Code of Conduct

Bug description

Adding folder sync with many subfolders throws unknown error in desktop client.

Steps to reproduce

1. Add folder sync with many subfolders
2. sync -> error
3. deactivate folders with many subfolders
4. sync -> success
5. activate 1 subfolder of many subfolders
6. sync -> success
7. activate more subfolders
8. sync -> error
   ...

Expected behavior

all folders and subfolders get synced without error

Which files are affected by this bug

any

Operating system

Windows

Which version of the operating system you are running.

Windows 11

Package

Official Windows MSI

Nextcloud Server version

31.0.8

Nextcloud Desktop Client version

4.0.1

Is this bug present after an update or on a fresh install?

Updated to a major version (ex. 3.16.3 to 3.17.0)

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

Are you using an external user-backend?

• Default internal user-backend
• LDAP/ Active Directory
• SSO - SAML
• Other

Nextcloud Server logs

not available (managed nextcloud)

Additional info

I am sorry, I cannot remove all the data that reveals personal identity from all the files in the debug archive. If you need the archive I can make it available to a not public address.

[bege10]

I just tested the scenario with v3.17.3. The issue is the same. So it is not especially related to v4.0.1.

[nilsding]

you can provide a debug archive here: https://cloud.nextcloud.com/s/Y6eJkdNt5BJYKcB

[bege10]

you can provide a debug archive here: https://cloud.nextcloud.com/s/Y6eJkdNt5BJYKcB

I just uploaded the debug archive.

[nilsding]

@bege10 thanks for uploading the debug archive

Seems like this is due to HTTP/2 requests not being retried if the server closed an earlier HTTP/2 stream. Found some warnings like these in the logs around the times any kind of network request is performed (i.e. this doesn't only happen during syncs):

[ warning qt.network.http2 unknown:0 ]:    stream 201 finished with error: "Server stopped accepting new streams before this stream was established"

The desktop client uses HTTP/1.1 per default unless the special OWNCLOUD_HTTP2_ENABLED environment variable is set to 1; could you check if that's set on your machine (or specifically for the application)?

[bege10]

@bege10 thanks for uploading the debug archive

The desktop client uses HTTP/1.1 per default unless the special OWNCLOUD_HTTP2_ENABLED environment variable is set to 1; could you check if that's set on your machine (or specifically for the application)?

Yes, it is set to 1. Setting it to 2 solves the issue.
I have different Nextcloud providers for personal and business Nextcloud. One of them - probably the one not used here - recommended to set this variable to 1. Does the issue mean that the other provider does not support HTTP/2?