I also had the same issue. I played the music while going to sleep. When i woke up the folder which I played ( sorted in title name ) which initially had 200 songs became 36. When I checked in file explorer, they have been actually deleted. All songs after the alphabet C were missing. I had experienced this same issue several times for the past 2 years. I thought it was an issue with the SD card. But it also happened on my brand new one. So, I figured out that poweramp had been deleting my songs all this time. Previously I tried checking for errors and formatting , but it happened again. My SD card doesn't have any issue. My folders doesn't have more than 350 songs.
Please take it seriously, and look into the issue.
I had my music file tags edited by Tagscanner.