As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT, THE CABIN ALTITUDE INCREASED TO 13,000 FEET. THERE WAS NO RESPONSE SWITCHING TO MANUAL/STANDBY ON THE AUTO PRESSURIZATION CONTROLLER. DIVERTED TO ATL WITHOUT FURTHER INCIDENT. FOUND THAT THE RIGHT PACK WATER SEPARATOR SOCK WAS DIRTY. REPLACED SOCK, PRESSURIZED AIRCRAFT SEVERAL TIMES WITH THE RIGHT PACK AND OPERATIONAL CHECK OK.