Bug with add. task (Assassin's Creed: Unity)

In part 5, mission 3 "Prophet", you need to make 3 stealth kills. I hide in a haystack, I kill the first one, from a haystack - it doesn’t count, I kill two more: I just crept up to the first one, I kill the second one from around the corner - and this also doesn’t count! What to do with it? Help good people...