While rescuing the Deputy in Primm, I ran into an invisible enemy that would randomly spawn and shoot at me. If shot he would despawn and respawn somewhere else, and if you try to use V.A.T.S. on him the Xbox Freezes. This happens regardless of the weapon equipped.

Has anyone else ran into this?

I encountered something similar. I shot an enemy and the body fell down but their invisible ghost(?) kept attacking me. I could not kill the invisible attacker and had to load my last save.