I used a Joker card in the Cathedral, went to a devil room, beam of light and trap door. I don't think I've unlocked the Chest yet, but I'm there.
Do you remember the colour of the fires in the Devil Room ? Were they Both Red Fires (the agressive ones) ?
Did you take the time to extinguish them ? Did they drop Black Hearts ?
I don't know (for now) if this is a particular thing, or just another Broken Devil Room (a Devil Room you can have if you close/open your game during a run). - Metarkrai