Hello,

I've got same kind of issue but it is quite frustrating:

I've got MMA for a long time on my S7 Edge. I have not changed the music I have for also a long time.
My usage is: a 128GB SD card, 20GB of music inside it. never used the internal memory for music.

Recently, I decided to erase all what I have and change my "long" playlist. I erased through a root explorer everything. I copied my music from my computer to my SD card trough MM (windows).

Then when I get back to MMA, I found out that it kept the old list of tracks I had. requesting to check new/change media, did not work.
I tried to remove the library folders, to add it them again. did not work.
I tried to uninstall, reinstall MMA + MMA pro, and then granting access to the SD card, did not work
but, when requesting to add music folders from the internal memory I got some mp3 (ringtones).

It is as if I did not grant access to the SD card, which is false.
I am going crazy with this problem...

Card could be damaged or is a bigger card that is only kind of supported by the device.

I formatted everything and started afresh since copying files across didn't work. It still didn't work so I'm guessing my new card must just be incompatible as now I've got it all working on the old card as before.

Did you copy files from the old to the new card (especially MMA files)?

Latest version of all (MMA Beta).

Yeah, I always worked with an SD card and it worked fine until I switched it to a new one. Now I have the same problem on both.

Which version of MMA, MMW and Android? Are you working with an SD card as it may be having issues.

Really starting to get frustrated with MMA now. Got a new SD card, had issues syncing via wi-fi (have never been able to sync via USB), formatted my whole phone and re-installed MMA to start afresh. I tried it first with just one playlist (2200 songs, previously worked fine). Sync went ok, but then when I went to the playlists on MMA the number gradually decreased, as in I could see it counting down on the display, stopping on 980. These tracks play fine and it seems like it only synced artists from A-G for whatever reason, although the sync itself never reported errors or got interrupted.

I really don't want to go back to Apple and iTunes but this is a pain in the arse.

EDIT

Just restarted my phone and now it says MMA isn't installed, despite me literally just having used it all night.