RN214 refuses to take snapshots

OK, to summarize: After reverting my RN214 to factory settings and creating home shares for a couple of users, snapshots (neither smart nor custom, no matter what schedule) did not seem to work anymore for the home shares of all users. Manual and automatic snapshots for other shares not related to individual users worked fine. There was no issue with insufficient space (no snapshot pruning taking place), analysis of the logs via SSH and by exporting them from the box did not yield any clues.

So I have created a new user "test" with all default settings in the "Users" group. The first visible difference were with ownership of (sub)directories, where directory "test" for user "test" is owned by the respective user and (sub)directory "Documents" of user "volker" was owned by root. 

root@rn214-volker:/home/test# ls -la
drwx------  1 test  users 46 Nov  8 07:45 .
drwxr-xr-x  1 admin admin 38 Sep 22 16:58 ..
drwxrwxr-x+ 1 test  users  0 Nov  8 07:45 test
-rwxrwxr-x+ 1 test  users  4 Nov  8 07:44 #test.txt

root@rn214-volker:/home/volker# ls -la
drwx------  1 volker users     396 Nov  8 08:10 .
drwxr-xr-x  1 admin  admin      38 Sep 22 16:58 ..
-rwxrwxr-x+ 1 volker users   92508 Oct 22 19:04 20211022_backup.log
drwxrwxrwx  1 root   root   187098 Nov  2 16:57 Documents

That might be due to the way I have restored the backup, i. e. by creating a trivial rsync copy job to copy from the USB3 drive directly attached to the NAS. Since snapshots should be taken by root, I figure that this is not a problem though. And files/folders are rw(x) for UG which should be sufficient. If not, a simple chown -R on the console will do the trick.

It got more interesting after finding out that for user "test" automatic snapshots are actually taken successfully, while at the same time, no snapshots for user "volker" are stored even though he is sharing the same schedule. As it happens to be, [X] Allow snapshot access was enabled for volker and [ ] Protection was disabled, user "test" had it the other way round. I don't think, (dis)allowing snapshot access is the big deal here, so let's have a look at what the manual says for the protection option. Well, ummm, not much: "Snapshots, if used, of content within the home folder are also within the home folder, with the same protection.". So it's probably about Bit Rot protection (copy-on-write) which is available on redundant RAID architectures. As the manual also states "could decrease performance", I have probably switched it off at some point.

Currently, I'm running a test with various combinations of (dis)allowing snapshot access and en-/disabling the protection feature, (de)activating bit rot protection and compression for the other shares to find out what exactly spoils the fun here. Stay tuned - screenshots of the respective menu options attached below.