[Bug]: Nextcloud client on windows writes null to files instead of original content

[dodancs]

⚠️ 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

The Windows version of the Nextcloud client syncs files successfully but replaces file content with null (see attached picture). It happens randomly.

I noticed that the issue mostly happens when I use a Nextcloud client for Ubuntu, and then when I switch back to Windows on a different machine, I can see that random files have been overwritten with null characters.

I tried to force-sync the files on the Windows client, but it says everything is up to date.

The files on the Nextcloud server and the Linux computer are still fine and are not affected by syncing of the Windows client.

Steps to reproduce

1. Use Nextcloud on Linux (Ubuntu 21.10 desktop)
2. Edit some files
3. Use Nextcloud on Windows (3.4.1, I later updated it to 3.4.4 but it did not do anything)
4. Notice some random files are now un-openable and when you examine their contents, they are full of null characters.
5. Shed enormous tears.
6. Grab your backup and replace the files manually.
   ...

Expected behavior

The files should be synced properly. I see no reason why the Windows client decides to overwrite the already existing and properly synced files with null characters.

Which files are affected by this bug

Any, I cannot predict which files are going to be destroyed

Operating system

Windows

Which version of the operating system you are running.

Windows 10 Pro 21H2

Package

Other

Nextcloud Server version

22.2.6

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

Updated from a minor version (ex. 3.4.2 to 3.4.4)

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

Logs do not show any trace of manipulation of the affected files.

Additional info

No response

[dodancs]

Nextcloud client Windows debug archive https://drive.google.com/file/d/1XoP8pXQqpLZU1yyed8_rkodF6vms5KsW/view?usp=sharing (couldn't upload directly, it's over 140 MB in size)

[dodancs]

The same happened to me today in Ubuntu.. The server version was fine but the local copy was full of 0x00 characters.

[dodancs]

Hey! This hasn't happened to me in a long time, so maybe it was fixed along the way in some version. I guess we can close the issue :)

[joshtrichards]

Closing per last comment.
Related: #5165