Did you Plex Dance the file? If you change the name while its still visible to Plex (in a folder Plex indexes) Plex will detect that it was a file RENAME and do nothing. So if the file is improperly matched before (or missing), it will remain so after the name change.
Alternatively, I have never added a file that Plex simply ignored. If anything happened, it probably matched to the wrong movie by mistake, or could have been mistaken as a duplicate file to an existing file. Filter for “Unmatched”, or filter for “Duplicates”, to see if it showed up like that. Filter by “Date Added” and look for unfamiliar files to check for a possible mis-match.
I think when I added the movie originally, it tried to match up as a duplicate of the 1989 “Batman” movie.
Edit: Did a quick search. Plex supports m4v, but people have had issues with files like it in the past. One such article says m4v is an extension that is basically mp4, but with the potential for DRM. Plex will not be able to play DRM protected files, so if there is DRM that might be why it won’t show up?
