I think, you still have to investigate which process restores the old version. Could it be that in a raid setup somehow the previous dataset has priority over the modification?
In any case, I would assume that something has been configured in an odd way on the network drive device. I would ask their support.
It keeps it if I do it with Explorer and set to Read Only, so I’m happy for that. It may be a BTRFS thing.
FWIW it’s not btrfs. My NAS runs btrfs on the data drives and I have no problems with tagging in any way.