As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DISCREPANCY: NO ENGINE BLEED AIR ON LEFT SIDE PACK WITH ISOLATION VALVE CLOSED (PACK NORMAL OPERATION THROUGH APU BLEED AIR) 515Z 8/28/21 MI. CORRECTIVE ACTION: PERFORMED TROUBLESHOOTING, FOUND PRSOV AT FAULT, REMOVED AND REPLACED THE PRSOV IAW AMM 36-11-09, OPS CHECK NORMAL COMPLIED WITH ETOPS VERIFICATION.