Invisible Kulemak

Happened to me twice,if killing the vessel of kulemak near a wall there is a chance the body will fall slightly outside and when revived it makes the whole boss invisible.
I could still hit him but at no point it returned visible again and i am mostly certain it is because the body is either outside the wall or touching the wall on the edge of the arena.

This happens to me when I cull Kulemak with triggered lightning warp. I have used the same setup with firestorm killing him and he is still visible next stage. But when the cull goes off he becomes invisible the rest of the fight