As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURNBACK WE INITIATED A DESCENT. PASSING ABOUT FL210 THE ALTITUDE WARNING HORN ACTIVATED. PASSING THROUGH APPROXIMATELY 15,000 THE PASS OXYGEN MASKS DEPLOYED & THE PASS OXYGEN LIGHT ILLUMINATED. FOUND NR 2 ENGINE PRSOV LOCKED OUT. REACTIVATED NR 2 ENGINE PRSOV IAW AMM.