I run Ubuntu server. Not Synology. My understanding is that you would need to go through the process like this:
https://forums.plex.tv/t/synology-faq-questions-answers-and-how-tos/490215/39
Except on re-install you would chose Normal Installation.
All of your existing libraries and database entries would remain intact.
I suggest that you try 1.41.3.9314.
