Plex Playlist troubles creating/showing playlists (Posted 4 months ago but for no replies)

So I'm starting to make playlists of all movies that have sequels. I have 11 so far but when I try to add a movie that I forgot, to a playlist (for example Superman 1-6 added .... but Oops, I forgot to add Man of Steel, I'll add it manually), Only 6 playlists show up to add to... it can't be a limit to movies in a playlist because I have 2,000 (and counting) shows in my TV playlist and it works perfect.
I've already deleted the playlist and remake the same one over again. And this is happening on both of my platforms (MacMini, MacBook).... Am I missing something?