First I thawed the freezer in totality. Seemed like a good time to clean everything too, then in my research I determined it was either the defrost heater or the thermostat kit. I ordered both. In the mean-time the fridge would work ok, except it showed dashes at stopped working. I assumed it was probably due to my original issue. That happened a couple days after the initial thaw. I got the parts and put my fridge into diagnostic mode. I tested the thermostat and it did fail (in the cold setting).I started by replacing the thermostat, then waited till the next day (when everything was at the correct temp, tested it again and it passed! This allowed me to test the defrost heater in the diagnostic mode and it indeed worked! I could see it got very hot and tested by putting some water on it and heard the sizzle.
All in all it was a relatively easy repair and I am happy to know more about my fridge. I am sending back the defrost heater. It is awesome that APP encourages this behavor so that you have the parts you might need when you are doing the repair job. I opted to not install the defrost heater because that looked like a pain (would realistically take 5-10 minutes, not too bad) compared to just the thermostat and I am happy I followed my intuition.