my upgrade was a nightmare .... took over 3 hours ... after a fresh, wipe boot drives, install everything looked more hopeful till a reoccurring issue rose it's head again, the system would not boot by itself after the config file was restored. throughout the process, when warm rebooting of the system, I would have to go down and turn it off .. let drives spin down .. and power up again. Never had any issue like this before since I built it.
Although everything (files/jails/settings) were there, Plex has been up to old tricks that were resolved in the last update.
In many years of updating f/w on my Qnap boxes and until now .... everything had been smooth sailing.
BACKUP that CONFIG file ......
Oh well ... live'n'learn ....