Thanks for the update.
The number is probably the Role id
for him in the Plex database. It is visible if you look in the XML Info for a movie:
Role id="46636" filter="actor=46636" tag="Gene Kelly" role="Pinky Benson" thumb="https://metadata-static.plex.tv/8/people/8c929d36b8a395d851fd4c7abd6e7b18.jpg"/
Since Gene Kelly appears twice, there are most likely two Role IDs in the database (same for other duplicate actors). Refreshing the metadata is supposed to clean up the duplicates.
A Plex Dance should fix the situation for a specific movie. However, I’ve no idea which movie should be “danced,” - one from the first listing or one from the second.
Could you try Plex Dancing two of the Gene Kelly movies - one from each sort of his name? Then refresh the metadata for the library and optimize the database. You can dance both movies at the same time.
If that does not clean up one of the movies then something strange is happening.
FYI, the Role ID for an actor is unique to a Plex Server. Gene Kelly will have a different number on your server.