As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: WHEN PERFORMING OXYGEN MASK OPERATIONAL CHECK THE FLIGHT ATTENDANTS OXYGEN MASK AT DOOR 4R FAILED TO OPEN AND DROP. REPLACED OXYGEN MASK CONTAINER / MODULE PER AMM 35-21-41 AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK.