A320 First Officer reported a pressurization alert resulted in a diversion to a safe landing. First Officer also indicated an operations engineering bulletin confused flight crew about the validity of ECAM alert.

Narrative

The flight started as a normal; routine flight. We reviewed the MELs; most were just placards; but one: 36-11-XX-X specified a unique procedure regarding the high pressure valve. We briefed the OEB61 Issue 1.0: CAB PR EXCESS CAB ALT and determined that if an excess cab alt alert appeared that we 'may unduly disregard the CAB PR EXCESS CAB ALT alert; or delay the start of the emergency descent when recard. The captain performed pilot flying duties while I performed Pilot monitoring duties. We followed the procedure for the MEL's procedure on taxi and takeoff; and climbed out normally. We reached cruise at FL340; shortly after cruising for a few minutes; a CAB PR SYS 2 FAULT message appeared on the ECAM. We evaluated the message; compared it with the OEB (Operations Engineering Bulletin); determined the message differed from the OEB. Within about 20 seconds of this message; the Flight attendants called: the captain took the message in which the flight attendants indicated that their emergency light for pressurization was going off; aural warning for depressurization was going off; and it was communicated that they might be having a depressurization issue in the cabin. Following this information; we immediately put our oxygen masks on; the captain indicated for me to take the flight controls; descend; and request that ATC give us a descent and a turn back towards ZZZ. We came to the conclusion that based off the CAB PR SYS 2 FAULT; the aural and visual warnings in the cabin; and the desire for the safest outcome; we agreed to descend to 10;000 feet to assure the safety of our crew and passengers. We were overflying our OA1 point and decided to [advise ATC] to remove any altitude or heading restrictions and allow us to return back to ZZZ rather than diverting towards ZZZ1. We agreed that given the stress of the situation and the possible safety risk of our passengers that reconvening in a holding pattern at 10;000 feet would be the safest decision to safely aviate the aircraft; determine our best course of navigation; and later inform ATC of our plan. Once we reached 10;000 feet; ECAM messages cleared and our pressurization gauges indicated normal operation. We held for about an hour to burn off enough fuel to get the aircraft below the max landing weight. We briefed over our plan; updated our route; and checked in on the well-being of the each other; our flight attendants; and the passenger on board. We notified dispatch; ATC; and made sure all of the appropriate sources were properly notified. Once below our max landing weight of 145;505 lbs; we notified ATC that we would like to head back to ZZZ. They rerouted us to allow us to safely navigate back to the airport at 10;000 feet; and joined the ILS via a few fixes and radar vectors. We landed safely and taxied back to the gate as if it were a normal operation. We debriefed the situation and determined that heading back to the airport was still the safest decision and were ultimately happy with the outcome of our decision-making.