Stirring den quest spawned only one critter, but wanted me to kill two.

I started a stirring den quest, destroyed the nest and killed the one and only critter that spawned, but the quest told me there were two critters to kill. This mysterious second critter did not spawn and did not have a marker indicating its location on the map. The timer ran out and I failed the quest since there was no second critter to kill.

Quest told me to kill two critters despite only one ever spawning, and it failed.

Either the quest should have required me to only kill one critter, or two should have spawned.