As an experiment, I copied a dummy mp4 file into my Movie library as “Man of Steel.mp4”. Plex picked it up fine.
Seems super odd that just copying your file to Man.mkv gets it to detect correctly. I tried that and Plex thinks it a movie called Hombre.
Have you tried copying a different file to “Man of Steel.mkv” just to see if its detected right? Trying to determine if its a Plex Agent issue or that file issue.
