I am a bit lost with this problem: I have a couple of TV Shows which have unmatched episodes although the series’ data is complete on TMDB and watch.plex.tv.
One example: Beverly Hills 90210. For this show, episodes S02E23 through S02E28 and S03E23 through S03E30 are reported as being unmatched and are missing metadata. Plex dance did not help and the problem could be reproduced with a separate test server instance.
The naming follows the naming conventions (e.g. Beverly Hills 90210 > Season 02 > Beverly Hills 90210 - S02E23.mkv).
Scanner and Agent are set to Plex TV Series.
Sometimes it’s the obvious! Thanks, @JaysPlex, that indeed solved it for me. I was not aware that there exists a 2008 sequel of that show. As for the other cases, it looks as if there are indeed episode entries missing on TMDB. I’ll contribute to the community project and add them.
Also thanks to @dbirch for offering help!