According to The Aviation Herald, the pilots fell asleep during the flight and were awakened by an alarm that was triggered when the autopilot mode was disengaged. The plane was then allowed to circle around and was able to land 25 minutes later.
Ethiopian Airlines has not confirmed the reports that the pilots fell asleep, but states that the plane in question “temporarily lost contact with air traffic control, but landed safely after it was resumed”.
The airline also advises that the affected crew has been suspended from operations pending further investigation and that “appropriate action will be taken based on the findings”.