Invisbile vile vulture

The Spires of deshar map.

No idea what is causing it, ive gone through this map at least 5 times already on diff chars and nothing till now. They seem to get near enough to pounce at you and then suddenly disappear and are not able to be targeted but when i get near them they suddenly reappear and will pounce at me.

Im using spark and flame wall. v confusing.

( ran the whole map seemed to me like they were somehow running up to me to jump distance and then somehow climbed down a invisible ledge kind of like how the ones hanging on the edges were )

the ones on the edge that were waiting for you to come near those never disappeared only the ones who were spawned on the map