I'd like to put this down now as an issue, although I'm yet to find a way to cause the problem.
The other day, while rehearsing, I somehow got to a state where the pedal up or down would cause the song selection to jump by exactly two songs with either up and down button presses.
It was impossible to get the cursor onto any song one, three, or five, etc. places away. Switching out of the playlist player and back in resolved the problem.
This occurred in v3.6.4 on my iPad Air 2 on iOS 15.7.1 using an iRig Blueboard pedal in MIDI mode.
If I'm alone with this problem, I'll report back if it happens again.