When I want to use Poweramp, I basically need to wait for a full rescan every time I've rebooted my phone, because Poweramp forgets the stored tag information for its entire database.
Sometimes I also encounter a similar problem where every (or almost every) song returns a "Failed to play track".
I'd guess both of these might have to do with delays mounting/reading the SD card, but that's just speculation.
Behavior seems very similar to what's seen on Android 7 on the FiiO M11, strangely enough:
I would blame my hardware, except other media players (like GoneMAD and foobar2000) handle it fine, so I think there must be a solution.