Missing animation? Spark?
I had to fix this on a character the other day. It was a block spark for a grenade special. Every time they would block a grenade thrown at them, or knock it aside, it would spawn a clone because it was missing the animation. Look for that. It might be something similar. Also, make sure that if it is a specific animation to the character and it IS there in the AIR, that the code has a S before the number so that it knows to look in the character and not the screenpack system (Example S100 or whatever.)
You may also want to check Metallo and see if the P2 state in whatever attack he does to cause that glitch, calls for an animation that Snake is missing.