Hi warrenfromnq,
I have had exactly same issues with rented movies with my IPad Pro as well.
My solution to free media file is to simply deleting Apple’s Videos app and then reinstalling the app from app store.
This simple method did free memory media file, and no longer displays numbers of movies in “about” section under setting.
Its been working without any issues so far, and this simple process doesn’t require restoring your device to factory setting to free media file as suggested in past thread.
Just make sure to backup whatever you have on videos app you don’t want to delete and you’re good to go.
l hope this helps out.