Unfortunately, it's impossible to reliably reproduce this problem. If you Google a bit though, you can easily find lots of results for files that magically disa

Unfortunately, it's impossible to reliably reproduce this problem. If you Google a bit though, you can easily find lots of results for files that magically disappear[0], and not just during upgrades. We were able to pinpoint OwnCloud after making a private folder for one of our guest laptops (which we normally use for interviews and visiting clients, that sort of thing), and then leaving the laptop disconnected for a few weeks. This was a folder no one had access to, and files disappeared and then later this state was synced to the client. It is definitely a problem with OwnCloud. [0] https://forum.owncloud.org/viewtopic.php?f=14&t=19138 https://forum.owncloud.org/viewtopic.php?f=14&t=19138