Abyss spawning infinite mobs

I just encountered an abyss spawned mobs endlessly.

Jungle Valley map
Abyss had 4 segments
ended in a spire
had an eldritch altar spawn where the spire died
after I clicked the altar, the formerly closed pit began spawning mobs endlessly.

They don't give XP or drop items

bug# 3,287,799,334

I need to find an image host to upload screenshot because the forums don't allow attachments :(