Diagnosis
The main control board has locked up or is receiving unstable power. This is a software/firmware glitch, not necessarily a hardware failure.
How to Fix It
Perform a hard reset. Unplug the refrigerator from the wall outlet. Wait 5 full minutes. Plug it back in. The display should initialize normally within 30 seconds. Test all control buttons.
If That Didn't Work
The issue may be a poor connection to the user interface (UI) board. Unplug the unit. Remove the display panel assembly by prying off the plastic trim. Check and reseat the ribbon cable connecting the UI board to the main board.
Heads Up
Do not attempt to reset the unit by flipping the circuit breaker. The power interruption must be long enough for the control board's capacitors to fully discharge, which requires a direct unplug or a 5-minute wait.