The issue may be caused by loose or faulty connections between the thermistor and the control board, or it may mean the thermistor is faulty. Refer to your owner’s manual to locate the thermistor, and ensure the wires between the thermistor and control panel are securely connected. If you do not have your original manual.
If the connections are secure, the thermistor and control panel will need to be tested to ensure functionality. Testing requires the use of a multimeter.
You may need the assistance of a specialist trained in Sub-Zero refrigerator repair to diagnose and replace the faulty components.