I recorded a video in case my description isn’t helpful.
If you have a song, with the same title, or slightly different title, Plex treats it as the same file.
So for example if you have:
Wait [Mono]
Wait [Stereo]
Wait [1965 Stereo Mix]
It will see them all as the same track, and if you rate one of them 3 stars, it will rate all of them 3 stars. If you have a smart playlist with songs that are 3 stars and haven’t been played in 1 month, it will put all three into that playlist. Once one of those tracks has been played, it will remove all three tracks, because it thinks all three tracks are the same.
This also extended to not just different mixes of a song, but also different versions of a song, such as bonus tracks on special releases.
This is also happening with tracks that are on different albums, as an example, Joel Plaskett recorded his 2001 record Down at the Khyber and then in 2021 rerecorded and released the album * Twenty Years Gone: Joel Plaskett Emergency Revisits Down At The Khyber*. When I rate a song with 3 stars on one of those two albums, that different recording of the same song appears with 3 stars, too.
Here’s the video posted on Google Drive, if you see this right after I post, it may still be processing: Screen Recording 2022-09-06 at 2.28.49 PM.mov - Google Drive