It could be related to a regression in plex server versions above 1.24.5
Have a read here: Plex video stops consistently on browser, not on app and Plex Web stops buffering after 2 mins causing playback to stop
The smart TV can have actually a internal browser, and then you are fully exposed to this bug. You can try to downgrade plex server to v1.24.5, see if it makes a change.
