It's the switch, stupid! I thought I had fixed the "door ajar" alarm problem in the previous video, but the switch was definitely defective. In this video I open up the switch to clean it with DeOxit, which seems to have really fixed it. I also show measurements on the replacement switch.

Switch part number is Frigidaire 21682900. I got mine on eBay. So now I have a spare while the old switch keeps working.