Diagnosis
The clock memory backup system has failed. This unit uses a capacitor or a small battery on the main control board to maintain memory during brief power losses. That component is no longer holding a charge.
How to Fix It
This is a known design characteristic. There is no user-serviceable fix. The memory backup capacitor is soldered to the main control board. To retain clock settings, you must plug the oven into a dedicated outlet that is not switched and consider using a small UPS (uninterruptible power supply) for clean, consistent power.
If That Didn't Work
If the clock resets even during normal operation without a power loss, the main control board is experiencing a more severe power regulation fault and is fully resetting. This indicates a failing control board.
Heads Up
A resetting clock will also erase any programmed custom settings. Sensor cook calibration and other learned data may be lost with each reset, potentially affecting automated cooking performance until the unit relearns.