Try pleace to use on of these sound as upper 1 voice
Accordion bank: P1 harmonica or P1 harmonica AT2 or P3 ACC piccolo
Guitar bank: P1 Slidepro or P2 Nylon pro2
There is more sounds problem
Set the volume value for upper 1 on 35 (by using the volumeslider for upper 1 sound) and play the sound with aftertouch
I have now testet 3 Korgpa2x with the same fault
The upper1 sound sometime total mute whenn using aftertouch
It can be a big problem playing these sounds when you are using a volumepedal
Poli