It may not be your problem. Unfortunately, the only way to verify if you have some other issue is to name the movies correctly
If they still fail afterwards, then you need to invest troubleshooting steps somewhere else.
When you use a naming format like this it may work for a long time. What’s may be happening is those items are showing up as duplicates to some other movie already in your library
You can check that by filtering the library for duplicates here
If you see any posters there you can click the 3 dots and “get info”. You will see the file names that are being combined
As you add more media, now you have more and more movies that could accidently be mistaken as a duplicate. Eventually you reach a point where that process becomes a certainty
Rename a few of the movies you’re having trouble with and Plex Dance them to see if they show up
