I was having the same issue, signed out of the Plex Server (not the pin sign-in from Switch User but the Plex Sign In). To sign out, Go to Plex Server from the Docker using right click and WebUI. Then sign in with your pin if you have one. Once on the Plex Server, Click on your User Icon dropdown on the top right and then SignOut. Once you do that it should ask you to sign in again on your plex account and then you should be good.