I checked online and found out that it should be the door switches. Chatted online with Heidi(?) in AppliancePartsPros.com. Very helpful. Confirmed that it should be a switch, and suggested I change out all 3 of them. She gave the exact switch part numbers to use. I looked at a YouTube video and realized I could not do the repair myself as I have a neck issue. My 22 year old son was able to fix it rather easily under my supervision, in less than an hour. The only thing we had to figure out was that to access the clips to remove the switches, he had to first remove the long plastic frame which held them behind the latch sockets.
Tips: (1) Two of the switch part numbers are the same although all three look the same. Make sure you note down which two are the same in the microwave as you remove them! (2) Take a picture of the connectors for each switch before you disconnect, so you know which connector to use for the two connections.