Completed 2 after getting lucky, 3.... well I've just given up on that, given up on all lvl 3 challenges in fact (except the Parkour This, finished that right at 0 lol). Seeing my name on a leaderboard is not worth my sanity.

I finally beat 2 stars today. Having a gun with a drum magazine and the caltrop grenades ability as operative helped me out a lot.

I just try to speed run it. If Heavy, just absorb the damage, ur team usually starts to distract about halfway through. For the hacks, go around and hid in a corner.

Easiest way to do it is to cheese it, start a level 1 and do it, then you're up against only level 1 bots who aren't terribly bright.

The AI for that is a [censored] joke!!

3 is impossible I went on a little rant (not on the forums) about it. The objectives are just TOO open.