I've used gone mad for a long time and occasionally had weird things happen with playlists but they usually resolved pretty quickly. Definitely seen a few cases where I thought I'd deleted something but it still showed up in the app, or playlists appeared to be duplicated or didn't have tracks (although sometimes it was host a case of a big playlist taking a few seconds to load. But it's always been sorted out in the end.
I'm on Android 9/Pie and syncing to an sd card so I can't promise my situation is exactly analogous. My GMMP version is 3.0 beta 11b. Here's what I suggest for troubleshooting:
* Delete all playlists from the device and make sure that's reflected in the app. (No need to mess with audio files.) Also be sure you check /gmmp/playlists/
" Make sure your scan folder in gone mad is correct (I imagine you'd want the root Music folder)
* Sync from MusicBee. Verify that playlists are present and correct on the device (with file manager)
* See if they've showed up in gone mad. If not, manually run a scan. If they don't appear after that, maybe restart the phone as a last ditch effort. (Unfortunately, it doesn't give as much feedback as it used on to what's going on with the scan, it host runs in the background)
* Assuming they do show up, check playlist contents in the app. Be sure to wait a few seconds for it to load, just in case.
Let us know how it goes. If it's still not working, you night need to take this to the gone mad developer