I have just added BattleStar Galactica (1978) to my Plex server. Sonarr which uses TVDB gets me the images and title of the shows that aired without any issues. While Plex draw a blank and can’t get me any of the info including mages. When I go to TVDB and look I too can get all the info for the shows, images etc. So why is Plex not able to sync properly? It’s kind of annoying. 
I cannot find the link but I’ve seen some posts saying there’s issues with some TheTVDB APIs. If so, this should be temporary (fingers crossed)
and here’s the link:
Nice thread. Just I have the same for one tv serie:
