As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT NOTICED CABIN CLIMBING AT A HIGHER THAN NORMAL RATE. AIRCRAFT RETURNED TO AIRPORT AND LOCAL MAINTENANCE DETERMINED. FLOW PACK NEEDED TO BE CHANGED. BOTH FLOW PACKS WERE CHANGED. ALL OPERATIONAL TEST ARE GOOD AT THIS TIME, PRESSURIZATION, NORMAL.