I too recently experienced the same behavior, so the bug is still lurking. That is, PLEX did not match movies that were properly named and had a corresponding entry in The Movie Database.
To correct this, I selected “Match,” “Search Options” and tried to change the Agent to something other than “The Movie Database.” For some reason, the Agent did not change, but a search of “The Movie Database” was initiated and the correct Match was returned with the search results.
I have no idea how or why this works for me, but it does. It’s also worth pointing out that this quirk only effected ±10% of my movies. The other 90% auto matched fine, without any input from me.