As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER TAKEOFF AND DURING CLIMB, AFT OUTFLOW VALVE STUCK IN THE OPEN POSITION, MANUAL MODE SELECTED AND STILL COULD NOT BRING THE AFT OUTFLOW VALVE IN THE GREEN BAND. AIRCRAFT RETURNED TO BLOCKS. AFT OUTFLOW VALVE CANNON PLUGS FOUND DISCONNECTED FROM A PREVIOUS WORK, RECONNECTED.