As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 5645 - ATB - LEFT ENGINE GENERATOR ON MEL, APU WAS INADVERTENTLY TURNED OFF DURING CLIMB. APU RESTARTED ON THE THIRD ATTEMPT, MAINTENANCE AND DISPATCH ELECTED TO RETURN TO ATL. CORRECTIVE ACTION: NO FAULTS OR MINIFLAGS FOUND ON ECU BITE. ECU WAS REPLACED PRECAUTIONARY.