Media Scanning is Endless loop - with Scan my library automatically enabled

As a rule of happy Plexing, do not use automatic library scans or scheduled scans of any kind.
Be certain that you have Disabled

  • Empty trash after every scan
  • Allow media deletion

Manual scans are great. Deleting things using Finder is great.
The Plex Dance is very important to fixing things like in your last question.
The final thing that’s really important is naming your files well.