Sort the library for duplicates. Since it is a sequel, Plex may have combined it with the original or Plex may have misidentified it and combined it with some other movie.
If it is combined, you can split it apart then fix match so it will be listed correctly.
If you are using the new Plex Movie agent, you can add the IMDB/TMDB id to the folder and file name. Plex will use the ID to match the movie, download metadata, etc. See Naming and Organizing Your Movie Files for details.
Plex Dance the movie if you change naming or organization.
