This is the same reason as here: LG 55UB820V-ZH PLEX is not reachable
The reason why you can still access your server is perhaps because you have put your TV’s IP into
Settings - Server - Network - ‘Advanced’ - “List of IP addresses and networks that are allowed without auth”
That way the TV doesn’t need to communicate with plex.tv (which it now cannot do anymore) to authenticate itself.
