As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AIR TURNBACK: AFTER T/O FUSELAGE DOOR WARNING LIGHT CAME ON. AFT CARGO DOOR INDICATION. ON INSP AFTER LANDING IT WAS NOTICED THE THE AFT CARGO DOOR HANDLE WAS POPPED OUT. THE DOOR WAS CLOSED BUT NOT LOCKED. AFT CARGO DOOR WAS FUNCTIONED AND CLOSED AND LOCKED. SUSPECT THAT THE GROUND CREW DID NOT FULLY PUSH THE HANDLE INTO THE CORRECT POSITION.