[Bug]: NextCloud Client is corrupting large excel files (Files_Lock is enabled)

[vagner-dias]

⚠️ 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

Scenario:
After migrating large Excel files (20+ MB) to a NextCloud instance with Files_Lock enabled, these files are getting corrupted when users try to work on them.

The issue occurs intermittently—typically when a user opens an Excel file, makes a change, closes Excel, and clicks "Yes" to save before exiting.

Current Setup:
NextCloud (NC): 29.0.5
Files_Lock: 29.0.1
Client: 3.13.4
Excel: 2021 (the issue also occurs with Excel 2019)

Dev Team:
Feel free to use the following spreadsheet for testing (all data has already been obfuscated).
TEST SHEET.zip

Steps to reproduce

1. Open the excel file
2. Change something in the excel file
3. Close the file and Click yes on "save before exit"
4. Reopen the file right after closing it and do the same process

After that Excel will trigger a warning saying that the file is corrupted and will ask to recover the file. It may not happen on the first time you proceed with that, but will happen if you repeat the process.

Expected behavior

Files should not get corrupted

Which files are affected by this bug

Excel Files

Operating system

Windows

Which version of the operating system you are running.

Windows 11

Package

Official Windows MSI

Nextcloud Server version

29.0.5

Nextcloud Desktop Client version

3.13.4

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

No response

Additional info

No response

[mgallien]

@vagner-dias Could you test again with the 3.14.1 release ?

[vagner-dias]

@vagner-dias Could you test again with the 3.14.1 release ?

I have ran two tests with the 3.14.1 release, and it is still corrupting the files. See the test videos below:

Test 1:

WTghWox1gh.mp4

Test 2:

1DeQWycAIu.mp4

[vagner-dias]

Just to add an important detail:
This only happens if VFS is enabled
If a new connection is created without VFS support, this error does not happen.

This seems to be related to #6933, #3456, #6190
see below:

timestamp without VFS:

timestamp with VFS (file is not broken yet)

timestamp with VFS (file has been opened/closed and it is broken now)