I just added a directory of MP4 files to my Plex server and did a scan on the library monitoring that directory; it finds no new files. These MP4s are ripped from a disk via MakeMKV and formatted with Handbrake - they are homeschool math tutorials. I've already done the files from one textbook - those were seen by Plex with no problem and I set them up into a playlist. Now I'm trying to get the next textbook set up for one of my kids and it's just not working.
I did manually update Plex via Putty this past weekend (my server runs headless); maybe I did something wrong?