I have found the fastest way to resolve this is to manually delete from the Plex Library every TV series from the folder that had been removed from it 5 days ago. These ghosts all show as Unavailable, but simply can’t be exorcised by expected methods.
The Plex Dance enabled me to keep the metadata in the other Library they normally live in.
The Plex docs and reports of similar issues on other posts suggest that this case has never been tested.
