We had a similar issue with our cooktop and it turned out to be a childlock feature that was not described in the manual.  When it locks up, is there a red light that comes on?  I am not in my bus so I can’t remember the exact control layout, but there are two circles next to each other in the control area for each burner.  Accidentally wiping across them turns on the childlock feature.  To turn it off, place a finger on each of the circles and hold until the red light goes out meaning the childlock is now off.  Hope that solves your issue.