This is even the default behaviour in Plex.
Maybe you didn’t refresh the metadata of your library, after you converted it to use the new Plex Movie agent?
Refresh Metadata of both instances of this movie now.
If they are still not fused together after that, use “Merge”. https://support.plex.tv/articles/201018248-merge-or-split-items/
You might want to put your vote onto this thread instead: [Implemented] - Multiple Cuts Of Movie
