Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can. 
The Basics
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Nextcloud Server version (e.g., 29.x.x): Nextcloud Hub 9 (30.0.1)
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Operating system and version (e.g., Ubuntu 24.04):
- Proxmox LXC Container
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Installation method (e.g. AlO, NCP, Bare Metal/Archive, etc.)
- Proxmox
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Are you using CloudfIare, mod_security, or similar? (Yes / No)
- `no
Summary of the issue you are facing:
I have the dektop agent installed on windows 11 and sync hundreds of game files between the local windows machine and nextcloud so that I have these files available on a second machine as well.
Local folder is linked (mklink /d) to the corresponding nextcloud folder.
This works fine for hundreds of files (journal files) in that directory.
A “helper App” for this game (Elilte Dangerous) is writing a “edmc-journal-lock.txt” file into this folder when it starts.
Immediately after, nextcloud complains that it cannot sync:
corresponding lines from logfile:
2025-06-26 09:54:36:641 [ warning nextcloud.sync.networkjob C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\libsync\abstractnetworkjob.cpp:223 ]: QNetworkReply::UnknownNetworkError "Unknown error" QVariant(Invalid)
2025-06-26 09:54:36:641 [ warning nextcloud.sync.credentials.webflow C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\gui\creds\webflowcredentials.cpp:207 ]: QNetworkReply::UnknownNetworkError
2025-06-26 09:54:36:641 [ warning nextcloud.sync.credentials.webflow C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\gui\creds\webflowcredentials.cpp:208 ]: "Unknown error"
2025-06-26 09:54:36:641 [ info nextcloud.sync.networkjob.put C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\libsync\propagateupload.cpp:96 ]: PUT of "https://nextcloud.domain.tld/remote.php/dav/files/username/Apps/Elite Dangerous/Journal Files/Elite Dangerous/edmc-journal-lock.txt" FINISHED WITH STATUS "UnknownNetworkError Unknown error" QVariant(Invalid) QVariant(Invalid)
2025-06-26 09:54:36:641 [ warning nextcloud.sync.propagator C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\libsync\owncloudpropagator.cpp:288 ]: Could not complete propagation of "Apps/Elite Dangerous/Journal Files/Elite Dangerous/edmc-journal-lock.txt" by OCC::PropagateUploadFileV1(0x2182826bef0) with status OCC::SyncFileItem::FatalError and error: "Unknown error"
2025-06-26 09:54:36:643 [ info nextcloud.gui.activity C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\gui\tray\usermodel.cpp:867 ]: Item "Apps/Elite Dangerous/Journal Files/Elite Dangerous/edmc-journal-lock.txt" retrieved resulted in error "Unknown error"
2025-06-26 09:54:36:643 [ info nextcloud.sync.propagator.root.directory C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\libsync\owncloudpropagator.cpp:1652 ]: PropagateRootDirectory::slotSubJobsFinished emit finished OCC::SyncFileItem::FatalError
2025-06-26 09:54:36:643 [ info nextcloud.sync.engine C:\Users\User\AppData\Local\Temp\windows-31590\client-building\desktop\src\libsync\syncengine.cpp:937 ]: Sync run took 146 ms
When I close the helper app, the file syncs fine.
So I’m assuming it is related to how the file is handled by the app but I’m not sure how to further troubleshoot.
Other files (journal files) in this directory sync fine and the latest one is also “open and continiously written to” by the game itself all the time.
Any help in further troubleshooting or fixing this is highly appreciated