For the past month or so, anything added to Plex is showing either that it aired on Jan 1, 1900 or December 31, 1899.
Weeks after TVDB and TMDB metadata has been approved, the dates for all media refuse to update. There has to be an issue with either the API or the scanner agent that Plex is using. It’s baffling how no one is working on this fix. I’ve confirmed with multiple people that they’re seeing the same thing.
I had the same problem, same version of PMS on macOS.
Confirming that upgrading to 1.27.0.5889 (Beta) and refreshing metadata as per dane22’s instructions fixed it for me.