Plex dancing one file is only meant to be a test. Whether or not it works tells you if you have some other sort of larger problem that needs more investigation
If it works and you’re able to reproduce it repeatedly I’m afraid there might not be a better option
I’ve never used them but I think there are some 3rd party tools like WebTools-NG, Tatulli or Sonarr that can find missing episodes
The only other option is to rename all your files and recreate the library. There are renaming tools that do this reasonably fast
