As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB ALL PASSENGER OXYGEN MASK DEPLOYED. AIRCRAFT RETURN TO STL. MAINTENANCE INSPECTED, CLEANED AND RESTOWED THE PASSENGER OXYGEN MASK. AIRCRAFT FLEW A MAINTENANCE CHECK FLIGHT AND THE ALITITUDE SENSING SWITCH WAS FOUND TO HAVE MALFUNCTIONED. MAINTENANCE REMOVED AND REPLACED THE ALITITUDE SENSING SWITCH. SYSTEM OPS CHECKED GOOD.