I got so fed up with this kind of thing happening with Rockstor, after the 3rd time of the system going tits up, I just installed an Ubuntu server, setup RAID1, LVM, ext4, samba and now solid as a rock. Oh and Plex is now fully up to date as opposed to the old version in the plex rockon. I can reboot or update it without worrying everything will break, and having to recover my data.
@wolf.f Cheers for confirming this in the testing channel update. I have reproduced here and it is currently under investigation. The testing channel updates version of Rockstor does and will break and is not recommended for production use. Linking to an earlier report of the same.
As you diagnosed this affects 3.8.16-7 release.
@William212 Those errors indicate an issue with the btrfs file system so yes a re-install may well help here if the issue is on the system drive, please see the Reinstalling Rockstor section of the official docs. Note that you may want to disconnect all your data drives during the re-install to avoid the risk of accidentally choosing the wrong drive to re-install.