Biggest issue for me is the metadata agent appears to be spectacularly bad at picking up air dates. Not an issue for most shows but anything with specials interlaced between series is a nightmare.
There are some nice things about it but really wish they had kept it under wraps until it worked properly.
The plex agents are only as good as the source data they scrap from. Also, if you have configured to use episode ordering from TMDB (which is the default) they have a VERY strict aired ordering rule for their episodes.
In saying that have you got an example?
Yep, and have checked that the episodes are matched properly and are correct in TvDB.
I could list heaps of shows but the most recent one I saw was Last Week Tonight. All other metadata is fine but no air dates.
Using your example you gave I ran a quick test and added the show with the last special from TVDB Last Week Tonight with John Oliver - S00E55.mp4 and it came into plex including the aired date. See below …
Also remember, there is no TVDB agent anymore, its a consolidated agent in plex now combining data from multiple sources to give the best metadata experience. Yes the ordering can be controlled based on your naming of episodes per TVDB or TMDB but the data itself is a consolidation.
Sure now make the magic trick work on a real episode 
Mine pulls in the data for the special too, but not the show.
Based on the Jan 1 1900 date I bet you have prefer local metadata enabled? Try and disable that and force a refresh.
I had my Libraries converted a few months ago, but have eventually converted them back to the old system because the new Plex database had wrong or missing information and no way to see or fix the source data, or override it on a case-by-case basis with an different database.
I wouldn’t mind converting back to Plex DB if Plex has fixed the issue not being able to match a single show to a different database like TheMovieDB or TheTVDB when the Plex database is inadequate.
I too want this notification to go away or an Opt-Out setting. I tried using the upgrade libraries and it seriously screwed my database up. Movies were being listed in the tv shows folder that were not there before. I get that maybe some tweaking might be needed to make my files work with it, but my library is tooo massive to spend that amount of time renaming stuff to make upgrade library work.
Everything works fine using the old system.
Ok, many new version have been released with the upgrade arrow still there. I wouldn’t mind an answer from a Plex employee if that arrow will ever disappear. Is there a plan to remove the legacy agent completely in the near future?
I still want the arrow to be removed, I think most people have seen it by now and know where to do the library upgrade by themselves if needed. Please remove it, it’s just annoying.
Yes, that is the plan and the reason why the notification was put there in the first place. So users are not surprised when suddenly the support for legacy agents is disabled.
It’s there to alert users and to give ample time to devise a conversion strategy.
The notification is a lesser annoyance, when compared to the sudden disappearance of an agent which served as the basis of a library for years.
Should you decide to take the plunge, I recommend to perform the conversion “manually” though (one library at a time, if there are several to convert):
Movies: https://support.plex.tv/articles/upgrading-a-movie-library-to-the-use-the-new-plex-movie-agent/
TV Shows/Series: https://support.plex.tv/articles/migrating-a-tv-library-to-use-the-new-plex-tv-series-agent-scanner/
Have they fixed the problem in the new Plex agents to allow one to choose TheTVDB or TheMovieDB databases when the Plex database fails to provide the data?
That is the reason I moved back to the legacy agent after first trying the new Plex agents.
This is the last straw, this stupid upgrade screwed up my entire meta data on my massive library! I’ve been so busy lately that I just upgraded when the notifications were present. What a mistake! 
Thank you very much Plex team! I’m not one really want to post negative messages but I’ve had so many issues with Plex in the last year, it’s getting ridiculous.
What use to be a beautifully working media server is now absolute trash! I didn’t pay to be a beta tester, I paid to have a stable working media server/player clients.
I have to now manually fix thousands of meta data entries that took me ages to input. Forget it, I’m finally moving to Jellyfin! it’s going to take me forever to get it working correctly again, but at least I won’t have to worry about it constantly breaking!
The problem with this is you do not have a generic Audio library type. Or the ability to cline a library to another scanner type and keep all of the existing poster art and metadata. Unless you do. I have a library of Teaching Company audio lectures. I had to use the music scanner. Ten “Artists” based on metadata that alligns to course type. 478 “Albums” for each lecture. I tried to make a new library and it shoe-horned a lot of these into some random bands.
So if PLEX is going to mess up a perfectly functional library (that will probably never be updated since I don’t collect those anymore), what do you suggest I do?
Do we have any time frame on when the legacy agent is going to be removed?
I moved back to using this due to the poor data supplied by the new agent, without an option to select which source of data i want to use, the new agent is worthless
I am certainly not going to try the new one again and risk the majority of my library having poor quality metadata/posters
Dear @OttoKerner Thank you for these insights into Plex plans.
Do you also know about any plans on allowing a different or new way of having a UI of bringing metadata into PMS, then?
There’s a whole ecosystem of 3rd party agents out there and a bunch of people using them - as you know.
Any news on this? The missing API of bringing metadata into my own library is a show stopper for me in many ways. I don’t want to complain… I’m just asking…
So will this new agent scan and update all our well prepared artwork to some other default thing at the next update? Because that’s what the update notes seem to suggest (‘this may take a long time’).
Is there a way to export a list of TV shows in a library? I know I lose 12 different series after the upgrade. If I at least had a list of what I had before and then could make a list after the upgrade I could find out why some aren’t there.
This can give you a neat list:
I take it that we won’t get this removed? I have converted all my libraries apart from the movies where Radarr just doesn’t cut it as long as I don’t download my movies thru the program. Sonarr is ok to use but Radarr just makes it a so much harder. The built in sub downlad is not even close to being an option.
Is there any plan to disable the option, for my part I’m well aware that you will stop supporting plugins one day. I just don’t need the reminder every single time I go into plex.
I bit the bullet and upgraded- no real problems. But if you don’t want to do that you can use an adblocker to get rid of the icon, this works too.
