[Bug]: Applications stops responding when syncing virtual files

[charredchar]

⚠️ 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

Syncing a file while using Virtual Files causes the application to lock up. The only way to recover is to delete the settings as force closing the client and reopening it automatically tries to sync again.

Steps to reproduce

1. After logging in select Add Folder Sync Connection
2. Select the root folder for Select a remote destination folder
3. Ensure Use virtual files instead of downloading content immediately is enabled before selecting Add Sync Connection
4. Find a file using File Explorer, right click and select, Always keep on this device, the client freezes.

Expected behavior

The file to sync and not lock up the client...

Which files are affected by this bug

All

Operating system

Windows

Which version of the operating system you are running.

Windows 11

Package

Official Windows MSI

Nextcloud Server version

32.0.2

Nextcloud Desktop Client version

4.1.0 alpha (20251214)

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

Fresh desktop client install

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

The downloaded log from `/settings/admin/logging` isn't showing any entries from times during the issue even though the viewer does... Unless I can find some other way of retrieving the logs I don't know how to share them.

Additional info

I attempt to run the program with --logwindow since I can't use the Create Debug Archive option with the entire client locked up. But no logs appear under the Nextcloud-logdir folder.
The client logs are from the roaming folder.

20251214_1414_nextcloud.log

[charredchar]

As I continue to work on finding a solution I've come across a couple of other issues with similar symptoms but does not seem to be the cause.
I ensured BulkUpload on the server was disabled, though it should be by default.
I do not have an upload or download limit set, this was also how it was by default.

One thing I find is that I can tell the client to Make always available locally it doesn't lock up right away, I can still browse the files. But as I try to copy a file to that synced folder it then locks up.
I also set up the share to not use virtual files to start with, selected a single folder to stay in sync. This works without a problem. If I then right click that connection and enable Enable Virtual File Support it enables and I have no issues at all. I can add files, tell it to keep a file/folder available, etc .. no problems.

This has all been tested on my desktop PC. I have other computers I need to set this up on so I would like to find the cause before proceeding with their install so I'm happy to test if anyone have some tips. I may also wait for the next major release before proceeding with the other installs since virtual files acts different from the nightly compared to 4.0.4 so we can work on a solution.