As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EXCESS CABIN ALTITUDE UPON REACHING CRUISING ALTITUDE, RETURNED. OVERBOARD EXTERNAL VLV MAIN FLAP WAS FOUND OPEN. OPERATIONAL TEST OF THE PRESS CONTROL & MONITORING IAW AMM 21-31-00-710-801-A, TESTED OK & PROCEDURES BY MEL 21-26-02 WERE APPLIED OK.