I have a very large Movie Library and I noticed not all of my movies aren’t showing in Plex. At first I thought it might only be a certain video file format that had trouble (.avi) but i realized that wasn’t case. I cannot figure out for the life of me any reason why that wouldn’t be visible in my Plex Library. They are named perfectly and aren’t any obscure movies, I was just hoping someone could help me with this. It’s a bit frustrating.
Most of the time the problem with Plex recognizing videos is naming and/or structure:
See this for movies: https://support.plex.tv/hc/en-us/articles/200381023-Naming-Movie-files
and this for TV: https://support.plex.tv/hc/en-us/articles/200220687-Naming-Series-Based-TV-Shows
Also without the names and structure you are using there is little that can be done to help you.
I’m having the same issue and all of my files are named in the same consistent format “moviename (date)” and it isnt about file format or container either. I Can not find a solution I have rescanned the file folder refreshed the NAS device refreshed the meta data. Still missing some and not others.