Sadly has been an issue with Plex on Apple TV for quite a while now, no fix/work around available, no confirmation if current codebase will be fixed or if the only solution is to wait until the “New Experience” client moves from TestFlight beta to full release (it’s been in beta now for 14 months at this point).
Best workaround that many have found is to use Infuse (paid app) until Plex is able to release a fix.