Strongbox keeps casting ice spikes - 0 monsters remain in the map

Type: "Frosted researchers strongbox of treasures"
Guarded by 0 packs of monsters
193% more rarity of contained items
Casts ice spikes
Map: forge
Location of strongbox: on a bridge close to where the boss is.

Opened it with my my corpsewade pathfinder, it kept casting ice spikes, never stopped.

Killed the boss, had zero monsters remain, it kept on going.

Edit: to clarify it never dropped loot, it remained closed.