I upgraded to Plex Server v1.31.2.6810, and the Plex server would no longer launch. I did not have any plex logs why the server wouldnt start. I checked the Windows Event viewer to see the windows log. It looks like its related to the local app path in the Windows Registry but when I rolled PMS back to the previous version everything returned back to normal. I use a Windows Computer to run the PMS, and the Synology NAS for the media files and the Plex Meta Data. The patch notes seem to have some IPv6 revisions. I dont believe I use IPv6, unless my synology NAS does. Any advice in particular to check/change since my server works fine in a previous patch.
Plex always makes logs, especially if you are doing an upgrade, you should have SOME kind of logs. It may not contain anything you think is relevant but please zip %LOCALAPPDATA%\Plex Media Server\Logs and upload them. (I am assuming you are running plex on windows based on your initial post)
Also if you rolled back, try upgrading again and then post a zip of that entire folder. You should have more than 1 file in that folder unless you moved the location of the folder in your configuration.