I have a problem with my daggers too but only because I am not able to backstab. I only once backstabed one guy but every other position behind a person doesn't count as his back.. I am testing it only on the first two legionairs. Is it because of the low skill lvl or because I don't go to their "back" what I think I do correctly.
It takes practice. When you are in position, the attack icon changes to a backstab icon. Using the new overhead camera view (b) is helpful for lining up your attack.
