As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE AT FLIGHT LEVEL 28K CABIN ALTITUDE BEGAN TO CLIMB. CREW ELECTED TO DEPLOY PASSENGER O2 MASKS. FLIGHT CONTINUED TO WSAP AND MADE AN UNEVENTFUL LANDING. UPON INSPECTION MAINTENANCE CLEANED OUTFLOW VALVE, INSPECTED DUCTING AND OPERATIONALLY CHECKED THE AIRCRAFT PRESSURIZATION SYSTEM. ALL CHECKS INDICATED NORMAL OPERATION. ALL WORK WAS COMPLETED PER APPLICABLE MANUALS AND AIRCRAFT WAS RETURNED TO SERVICE.