I think this discussion deserves its own thread. I've read that Plex has had some issues with meta data not updating correctly. This particular thread is a good reference: https://forums.plex.tv/discussion/225873/problem-to-retrieving-metadata-from-tvdb/p1
I'm using the new My Passport Wireless Pro and I essentially had to throw in the towel and delete my TV Show library. For the short term, I've given up on including any TV Shows.
Before throwing in the towel, I've tried everything including multiple rebuilds but I can NEVER get all of the meta data to update on the Plex server running on this device. I believe there is a serious problem that needs to be resolved. Whatever the underlying problem, the MPWP becomes very unstable and often locks up forcing the user to hard power down leading to potential drive damage. With my TV library deleted, and database optimized, the performance is remarkably better.