Forest tower map + Vile Vultures invisible in the stairs

Not talking about the ones hanging on the sides that jump up!

Observed several times that on the intersections between paths and "round rooftop rooms" they will not be visible.
They can still hit you and they will block your move.

If you step backwards (cannot always dodge roll though) they will pop up and you can see them.

They sometimes spawn this way and sometimes they will be in the room/pathway and just disappear out of nowhere if you happen to stand in the spot where they will stop moving towards you.

It seems it happens when they go "up" stairs.