Strongbox with no monsters

Had a strongbox in the Rupture map type that did not have any monsters spawn.

When I clicked on it I immediately dodge rolled backwards used Forge Hammer, Infernal Cry, then charged up a Supercharged Slam. In case player actions caused it.

After letting the slam go I approached the strongbox and it just opened after nothing was killed.

In game bug reference number 1,478,016,387

I have had this happen twice today. Stronbox just opens and drops loot without spawning monsters. I was in two different map tilesets, Wayward Isle and I forget the other one. One of the maps had shocked ground.