Refrigerator and freezer not cooling intermittently

General
1

Please make sure to click on General above and select the correct appliance type first.

Brand: GE
Model Number: ZFGB21HZCSS
Main Symptom: Not cooling the fridge or freezer
What happens & when: It is intermittently not cooling the fridge or freezer, running about 10 deg above set temp. During that time the digital readout is dark (indoor light still comes on). Then after awhile it may start cooling again.

Error Code (if any):
Parts or tests already tried: In researching it looks like the best approach is to replace the control board, heater defrost assembly, defrost thermostat and temp sensor or sensors. I can see how to replace these parts except not sure if I need to replace all 3 temp sensors and unclear where they are located and how hard it is to get to them.

Please advise if I am on the right track or missing something.
Photos / video link:

2

Let’s start with what is running when it is trying to cool. If the compressor, and fans are running but it will not pull the temperature down, it is probably a sealed system problem. If it shuts off and nothing is running, then it is a temperature sensor. The defrost heater system would not be involved unless you tell me the evaporator coils in the freezer are iced over.