Which agent are you using? I was having trouble with TheMovieDB and TVDB recently - particularly around anime or recently aired shows. Some discussion of it here: Refresh metadata for one TV episode or recently added episodes
It was random for a bit but there was indication that TheMovieDB was having hiccups with Plex Proxy for the metadata; inconsistent for old vs new shows and I noticed it more with anime. TVDB was having similar issues for me as well but seems to be cleared up now but TheMovieDB is still acting up for some TV shows - and definitely anime.
