I have been experiencing the same issue starting today.
I had the first few seconds of a movie and then the Plex app shut down. When I started the app again I got this message.
I am getting this message on all my devices except from web play.
The server and apps are up to date. I already had the new player option turned off because I was unable to play anything.
I tried rebooting the server, the app, unlinking the devices and reinstalling the app without any success.
