Sorry to resurrect an old thread, but I finally got around to jotting down my notes on this issue. I've just sent the same text with a log from the app as well.
I've been having this issue for years (literally), but I've put off reporting it for a way too long.
The issue first started occurring spontaneously and not in relation to a hardware change like a new phone or SD card. Unfortunately I don't recall the version this started happening in because I didn't report it at the time.
I'm currently on build 939
Samsung Galaxy S9+
Android 10
General observations:
The files are actually removed from the library. Sometimes the song I'm listening to just stops and disappears from the library when a rescan decides to remove it. The removed files usually reappear on the next scan, with new "Added to library" timestamps, making my favorite sorting option useless/cumbersome.
The missing files are also missing from playlists (they're all .m3u playlists). To reappear and be playable I have to remove the .m3u-files, rescan, put the .m3u-files back and rescan. The "Rescan / Resolve Playlists" function does not seem to handle cases like this.
My phone is not restarted shortly before this happens. The SD card has been operational for hours and days when this happens (current uptime 676 hours).
I do not have any other music players or other apps that access the same root music folder, at any time.
The affected folders/albums are usually grouped (although still a random selection) in the sense that there are several missing albums from the same artist. See below for example.
For reference, my files are generally organized like this:
\SD card root\Music\Artist or Label\Album\##-Song.mp3
Description of actions and result in this particular instance:
I added a few new files to my SD card, in new folders, and did a manual rescan (I've disabled automatic rescans because of this issue). I then made another change to one of the same folders and did another rescan. When it finished, several older albums appeared as "Recently added". Half of these folders I have not even touched recently (for instance, all folder and file timestamps are from January in the Kim Petras folder).
Kim Petras: 6/6 folders affected
SPYAIR: 2/7
Fit For a King: 2/2
All That Remains: 2/2
Renraku: 1/5 (I deleted some files and folders here, but did not add any)
Spor: 1/17
TurboAutism: 1/2
These folders do not have any similarities to each other in terms of timestamps or the like.
