As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER LEVELING OFF, THE CREW RECEIVED A GROUND AIR DOOR PROXI SYSTEM CAS MESSAGE. THE CREW FOLLOWED THE QUICK REFERENCE HANDBOOK AND RETURNED TO PHL. MAINTENANCE INSPECTED AND FOUND FOREIGN DEBRIS ON THE PROXI SENSOR, THEN REMOVED THE DEBRIS. OPERATIONAL CHECKS WERE PERFORMED AND THE AIRCRAFT WAS THEN RELEASED FOR SERVICE.