It's not Plex who broke it per-se. Google removed the search APIs that Plex's TheTVDB agent used. When there is not a 100% perfect match with the TheTVDB title, the agent did a series of Google searches to find near-miss matches that it could then present as possible matches. It can no longer do that. If you check your log files (
\Plex Media Server\Logs\PMS Plugin Logs\com.plexapp.agents.thetvdb.log) you will see the queries to
ajax.googleapis.com and the errors that it produces.
I think that whilst Freebase was working, it covered up the gaping hole that left. Now that Freebase has gone, it's really visible.
Plex need to switch to the newer Google CSE API - but that is a paid service for more than 100 searches a day.
Their other choice is to improve their own matching engine against the copy of the TheTVDB they use to allow partial matches.