There is a problem potentially leading to data loss when using the Virtual File System in the ownCloud Desktop Client for Microsoft Windows 10 in the versions up to 2.7.2. We apologize for the inconvenience. We already have a fix with the ownCloud Desktop Client 2.7.3. We would like to urge you to update immediately.
The root cause of the issue is the incorrect handling of a change to the Microsoft Cloud Filter API which was introduced by a Microsoft Windows 10 Upgrade earlier this week. When the ownCloud Desktop Client for Windows recognizes new items for syncing, the folders will work correctly but, due to errors during the creation of placeholder files that are then incorrectly handled, the virtual files are not showing up. On the next sync run, those files are then erroneously marked as locally deleted and are subsequently deleted on the ownCloud Server, leading to loss of data.
Windows 10 versions prior and including build number 19042.662 are not affected. Branded ownCloud Desktop Clients up to version 2.6.3 are not affected because they do not include the Virtual File System. On Mac and Linux, the implementation of virtual files is handled differently and does not produce this error.
What to do now
Short answer: install ownCloud Desktop Client 2.7.3. If you have used the Virtual File System feature, please check if you are missing any files – and as an admin, please advise your users to do the same. If you have a proper trash bin setup, users can recover files that were deleted by restoring the affected files from their trash bin. Please check your setup and configuration in that regard.
Please consider that the available size for deleted files is affected by the quota settings for users. If you allow the mounting of external storages such as Windows Network Drives, any deleted files are using the ownCloud primary storage that might not have the size needed.
Again: Please update immediately.