Void Seed Problems on Abyssal Depths? Anyone else having these problems?

This has only happened to me 3 times, all on Abyssal Depths.

When the void seed spawns in, I am able to kill all but one void monster. Twice now, the last void monster wouldn't even show via marker, and this last time the marker was pinging the air, there was no monster in the vicinity, but it kept pinging the spot in the air.

It's pretty annoying, not game breaking, but I'm irritated. Is anyone else experiencing this?