Same here, multiple tracks showing up on All Songs. Symbols used to split are ; // feat. ft. w/
The number of times it is duplicated seems to be number of artists of the track plus one. I think it shows the track each time for every artist (including one for multi-artist).
Piggybacking on this, the artist's images is also kind of broken. Artists who are part of multi-artists track seem to have the same image. Looking into the com.maxmpzaudioplayer/files/artist_art/ folder, I saw that the "same image" file was named <Artist1>_ <Artist2>.jpg. I tried setting the image manually for both the artists, but it does not do so. A file <Artist1>.jpg and <Artist2>.jpg do get saved in com.maxmpz.audioplayer/files/selected_artist/. I have checked to make sure Storage permissions are allowed. Artist images for single-artist track works fine.
Version/Changelog: build-899-arm64-play [899004-6b777921]
Device Model: Samsung Galaxy S10e
Android Version: Android 11 / OneUI 3.1