As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INTERMITTENTLY, THE PILOTS 4-WAY TRIM SWITCH WOULD FAIL WITH AUTOPILOT ENGAGED AND WOULD CAUSE TRIM FOR AUTOPILOT TO TRIM PITCH UP, DISCONNECTING ANY OTHER PITCH MODES AND TRIM FULL NOSE UP ATTITUDE IF AUTOPILOT WAS NOT DISCONNECTED. THE CAUSE IS APPARENTLY THE SWITCH PHYSICALLY BROKEN INTERNALLY.