Abyss pit spawns infinite monsters

Report number 3 074 450 524.
I was in an Abyss encounter in map, and it spawned a spire. I destroyed the spire, but a pit next to it never closed and kept spawning new waves of monsters.
I stayed there for a minute or so to be sure, and later returned after clearing the map and the pit was still going.

Edit: Another occurrence with report number 4 132 445 001. This time there were two abysses with spires, but only the second one resulted in an infinite pit.