Another thing I just noticed.. When I play songs, the message 'Failed to play file!' always appears, although the song does play.
After 5(?) 'failed' songs, Poweramp automatically stops, saying too many songs failed to play.
This didn't happen on my Moto G5 Plus
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Looking more closely.. Poweramp appears to be skipping a song when I advance to a new song (with the 'double right arrow' button), then it plays the song after. (e.g. I'll advance past 'Happy Birthday', I very briefly see the song 'Starspangled Banner' sweep past, then Poweramp moves to 'Sing song whatever', and does play 'Sing song whatever'. And, it reports that 'Sing song whatever' is the song that failed to play.)
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And, I just deleted a folder with many MP3s in it (1000+?) [via a USB connection on Windows] and Poweramp was no longer finding any music with a rescan or full rescan (0 songs, 0 folders), so I force stopped Poweramp and reloaded it and did a rescan and it found mp3s, and now it is playing music as expected, without skipping. But, I am still unable to see any subfolders. I hope this helps..