Fortunately, it seems that rolling back to the more stable 4.5.4 release works well. 5.0.0.1808 was a disaster for my TS-563. Luckily I stumbled across the fan / system temperature issue right away and was able to get it logged along with the DNS issue which also plagued this unit and some others. I did have a 3rd issue after rolling back with the Malware Remove app not running, but QNAP support was quick to provide the solution (simply manually reinstall). I must say they were quick to respond to all 3 of the cases I entered. Based on the number of systems affected, you could hardly qualify this as a beta release let alone a "real" release.
Normally I am not one to jump on an update, but a couple days before I had put on 4.5.4.1800 and when I saw there was a x.x.1808 I didn't notice the 5.0.0 part (pretty stupid of me) so thought it was a minor update so slapped it on. Rolling back with 35TB of data was not a fun job. I do have backups, but it would have taken a few days to restore that much data. Fortunately it was not required.