I have noticed that when Surveillance 2 is trying to shoot someone with Surveillance 3, it can throw off the game's perceived "hit-detection." It's prompting you that you cannot tag, but while this is happening you often cannot get hit-detection either. It has happened a lot, with a variety of weapons, but I chose a short clip which also shows (aside from "missing shoulder and head shots) that the "No Tag X" prompt becomes permanently on screen after death...Does Crytek do QA?! I think not...