As funny as that is I fixed it now
I don't change settings. (rechecked it's normal)
And just when everything around burning and wheels explodes nearby fps drops significant and especially when many wheels also near.
I just can't focus (some times even see) on TB to kill him. Best max damage delta when player "dead" for couple of seconds before respawn and boss holds on position but guns still alive and can fire... (I used miniguns mostly)