I just encountered my first cursed chest bug. finished the timed even to clear 5 waves in time, done that and it was stuck at defeat all enemies. cleared everything many screens surrounding it, ported out and back in - still wouldn’t complete. I ended up giving up then continue the dungeon, found another cursed chest which I done and looted just fine, went back to the first one and it was now lootable. seems to have been linked to each other somehow or purely coincidental.
Thank you RobbieDe. This happened to me today as well in Shrieking Caverns.
If weren’t for your post I would have spend a lot more time or even quit the game to log back in. Your post saved me the loot. The bug is weird to link two cursed chests together.