This is a sign of a poor soldering connection inside the amp. Unless you have technical skills in electronics and the needed test gear, you would be bettter sending it off for repairs.
The easiest way is to get a translation dictionary for whatever language it is currently in and find the word for SETTINGS and LANGUAGE. Then change it back to English.
Hi, there's DEFIANTLY a problem with the touch screen, in my considerable experience, I've seen friends with the same model and they've all taken them back and upgraded to a higher model. I hope this helps. Regards, Neil Crook.