I may know what happened to you! At any rate I figured it out with my new instance. The problem is that the program can no longer get a media provider list from Plex. It tries to reach this resource at https://plex.tv/media/providers with an X-Plex-Token (google it if need be) as authentication. That URL is now returning a 406 code. You can try it yourself at https://plex.tv/media/providers?X-Plex-Token=YOUR_TOKEN
So I think your system needed to update its media provider list for whatever reason, and now it’s screwed. The program caches this info, so other people running the rpi plex client may be on borrowed time until they need to refresh.
Because I’m running my own Plex server instance, I was able to work around this by substituting the URL for its media provider list and then hacking the JavaScript around it to work with the response. I could post a modified server.prod.js for others to use but I don’t know how useful it will be generally. It would not work for cases where you want to get a media provider list from someone else’s server, for example, unless you could get them to give you their (hopefully static) IP address and server ID etc.
However, if someone who knows more about current Plex endpoints for the media provider list could chime in, perhaps we could get a more general solution out there. Hope this helps.
