Plex apps often obfuscate revoked sessions as generic server or library disconnects. Please enhance client side error handling to detect invalid sessions. Automatically present a login form whenever the session is invalid. At a minimum, show a clear error message about the session being invalid.
Various Plex client apps effected, including Plex Roku.
As a workaround, manually signed out and back in. But many users will instead be confused, wondering why their libraries fail to connect.