2 movies ... both mkv ... one found other ignored

Hello,
I run a Ubuntu 20 HomeServer with Plex and normally I really love to use Plex for my HomeCinema.

Right now I uploaded 2 new Videos … both are mkv … both same transcoding, same rate, CHMOD, Owner, all is same … why Plex can find one and the other get ignored and I can’t move it into my Library?
Why Plex don’t show me all my uploaded Movies? It’s not the Job of Plex to select what he want show me at my Library … so how I can solve it?

This problem I have sometimes … its very rarely for me but today it really makes me angry and I think about stop using Plex because it waste my Time. Anyone here have a Idea or Solution to solve this Problem?

Adding to Otto’s response…
Have you checked the other video hasn’t accidentally been mismatched as a duplicate of another item (e.g. using the Duplicate filter) or was simply mismatched (sorting the library By Date Added and checking if any of them don’t belong)?

I got it … It was a chmod Problem … I fix it already. Set the movie file to 755 and all is working well.
Thank you for supporting.