When a new Library directory is created at the top of the Plex share, it is completely independent and self contained. You can fully replicate everything you had before (makes the most sense).
Since you’re now running in the new Library successfully whereas the old did not. I don’t recommend going back to it. It’s corrupted down deep somewhere.
I therefore recommend deleting Library.SAVE and moving on.
As a point of order though, enabling backups of your database (Scheduled Tasks) is a good idea 
