The new agents Plex uses are more picky as to how the file needs be named. What worked previously may not now.
The only other thing to check is to make sure you don’t have embedded metadata in mp4 files causing them not to match properly. You can delete that metadata in each file if it’s there or disable “Prefer local metadata” in the properties of the library
If that’s the problem you have to plex dance after you change the setting
I would rename whatever needs it now. You can fix match items but if you ever rebuild your server again this process is going to start all over again
