Since the button seems to be sticky...
If this is a membrane or rubber push button, and you don't mind slicing into it...
You may discover contacts which have become dirty or corroded or gooey. Either metal traces or carbon pads.
Cleaning might solve the problem. It's an obvious thing to try, because it is easier to access the control panel than to get at the machine's innards.
I would cut a flap in the button. In the manner shown.
Note: This operation could ruin the button's operation altogether if you're not careful.
On the other hand, if it works you're a hero. Decide wisely.
Lift the button flap. Use any of several cleaning techniques. Use a solvent that leaves no residue. An easy way is a cotton swab and alcohol.
Do not use solvents which dissolve plastic. No acetone, lacquer thinner or fingernail polish remover.
Avoid soaking the area with so much fluid that it leaches under the membrane.
Avoid leaving fibers or residue on the contact area.
Contacts may get damaged so as to be unusable. Consider attaching a piece of aluminum foil to the underside of the flap.
Let the contacts dry. Put clear tape over the flap.
If cleaning doesn't solve the problem then the problem could be a broken contact. Or it may be in the machine's brains.