@tobiasKaminsky Yup, tried it and the issue remains. Also found a device with 3.13.1, and it too is affected now, so this now seems more server-related, though it is weird that the desktop client hasn’t been affected at any point. I would have assumed both clients employ the same webdav commands (and thus fail or succeed just the same).
Syncing a folder in Android app’s ”all files” view also still works (i.e. downloading changes causes no issues).
I have another server instance on another host, and there uploading from Android still works. This (working) instance is unencrypted, while the non-working instance has server-side encryption enabled.