As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE CREW RECEIVED A CABIN HIGH ALTITUDE WARNING MESSAGE, CREW RAN QRH AND REQUESTED A LOWER ALTITUDE AND RETURN TO KVNY. NO EMERGENCY WAS DECLARED NOR EMERGENCY DESCENT REQUESTED. UPON RETURN MAINTENANCE FOUND MED SEAL PRESSURE REGULATOR OUT OF LIMITS. REGULATOR REPLACED WITH SERVICEABLE ONE AND TESTED SATISFACOTRY.