When ticking 'Reset' on the Tone controls screen sets the bass and treble control fully ccw, suppressing the low and high tones. I would expect these controls to be set to the middle or neutral.
Folders rescan does not fix that. I removed a lot of files from the sd card while it was taken out of my phone and inserted in my computer. I could not find any rescan option to have Poweramp detect that files were deleted. A painful omission in my opinion.