Are you comfortable with SQL queries?
If you are,
Shut down your server,
make a safety backup up the main plex database file
then perform this query on the database
DELETE FROM media_provider_resources
(make sure to copy it in full, or there might be unwanted consequences, up to a complete data loss)
If you don’t know how to perform a SQL query, use either a SQLite database editor
or use the sqlite which comes with Plex server. Repair a Corrupted Database | Plex Support
