As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW EXPERIENCED AUTOPILOT WARNING AND INABILITY TO OPERATE THE STABILIZER TRIM MANUALLY - AIR TURN BACK. TROUBLESHOOTING CARRIED OUT THROUGH AMM & FIM INDICATING STAB TRIM CONTROL MODULE FAILURE. BOTH STCM'S HAVE NOW BEEN REPLACED AND IN PROGRESS OF REPLACING THE STABILIZER TRIM ACTUATOR. FURTHER UPDATE ONCE COMPLETED TASKS.