Since update 1.3 on xbox one my stealth kill animation does not seem to be working. Instead of stabbing them, whenever i hold the button the person just suddenly drops, no animation. I am not sure if this is messing with anything else such as the stealth kill achivement, but i figured i should at the very least report that the animation itself is broken.
Though i will say this makes stealth kills extremely efficient, you can easily take out groups of enemies in a few seconds.