Diagnosis
Moisture or grease seepage under the capacitive touch panel or a failing control board.
How to Fix It
Unplug the unit. Clean the entire touchscreen surface thoroughly with a dry microfiber cloth. Then use a cloth lightly dampened with isopropyl alcohol. Ensure no moisture remains in the seams.
If That Didn't Work
The touch panel membrane is likely damaged or delaminating. This requires replacing the entire front control panel assembly.
Heads Up
Do not use glass cleaner or harsh chemicals on the touchscreen. They can damage the coating and make the problem worse.