Plex Documentation → Your Media → Naming & Organizing Your Movie Files
How are you naming the file?
Seance 2021 is a movie. Plex uses IMDB.com and TheMovieDB.org IDs to match movies (it uses TVDB and TheMovieDB IDs for TV shows)…
Try naming the movie using the IMDB ID in the folder and file name:
/Movies/Seance (2021) {imdb-tt11188624}/Seance (2021) {imdb-tt11188624}.ext
Plex Dance the movie after renaming. It will clear incorrect information from the Plex server database.
