If you are having trouble turning in on then i know what this will be.
The control board is coming out of the holder so its not sitting right up against the glass top so doesnt pick up the touch.
Ive see this loads of times and its a simple fix if you are handy at diy repairs.
You need to remove the hob from the unit and turn it over so you can access the bottom.
Make sure the power is off and then remove the metal cover on the bottom of the hob.
Once this is off you will see the touch control board sitting in the plastic frame of the glass.
Look at the opposite side of the wires on the board and you will seee this is falling out of the plastic frame.
Push it back down into place and thats it.
Refit the cover and power it back on and it will be fine from there.
Try that and see what you find as ive seen this fault loads of times and its always down to the control board moving out of the plastic frame.