Strongbox Not Spawning Monsters

t15 Delirious Forge Map.
Strongbox is on a narrow bridge.
Identified used an Augment and Regal on the Box

Researcher's Strongbox
Guarded by 7 Packs of Monsters
Casts Ice Spikes
Contains an Extra Djinn Barya
Guarded by 2 Pack of Magic Monsters

0 Monsters left on map.
Seems to be a bug.