[Invincible glassed Orb Vallis jackal enemy]

I just experienced the same thing whilst doing Thermia Fractures. I was using Mesa Prime with a Fulmin. It seems the glass crystal on the face somehow has it's hitbox within the Jackal's hitbox. I did not have an explosive weapon with me, but i'm assuming that an explosive weapon wouldn't even do the trick (maybe the hitbox is not even there, who knows).