Following is info on this switch type.
REI - Technical Info: Basics of a Membrane Switch

If you want more info just Google "membrane switch" or "membrane key"

1. Heating up the key causes the parts of it to expand.
Odds are that there is a hairline crack and expanding the switch parts closes the crack so the switch works.

2. I do not know as I have never tried this.
It depends on what kind or membrane switch it is.
Also these keypads are not made to come apart.
You would have to cut around the start switch with an exacto knife or scalpel.
Being very careful to only cut the plastic and not ant or the underlying circuits.
Then find the cause of the switch malfunction and repair it.

There a numerous types of membrane switches so it may not be repairable and in the end the keypad would not look pretty.
Also it will no longer be water proof.

I would just replace the control panel.
Part number: AP3606066

You are welcome.

It never hurts to take things apart and sometimes you can learn stuff that comes in handy in other circumstances.
Bubble keys are also used on many other devices.
For instance I have been successful repairing them on remote controls etc.