I have a problem with the .mp4 files. If the film is embedded in plex, the title is displayed with the file name. when i convert the file to .mkv it shows correctly. My Agent is Plex Movie. That was not always so. But I can’t say exactly since when this has been the case
Sounds like a case of embedded metadata in your mp4 file.
If you want to rule that out, disable Prefer local metadata in the advanced tab when editing that particular library.