As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFT CARGO DOOR SHOWED OPEN ON EICAS DURING CLIMB OUT. UPON RETURN TO THE FIELD THE CARO DOOR PROX SENSOR WAS REPLACED. AIRCRAFT THEN FLEW 3 ADDITIONAL LEGS ON 10/15 WITH NO ISSUE. ON THE 4TH LEG THERE WAS A REPEAT OF THE OPEN INDICATION AND THE INDICATION WAS PLACED ON MEL.