So, just to be clear, are you saying that when using Surge you are able to kill the mech while it's facing away from you but the game doesn't count it? Or are you saying that you are often unable to complete the kill while it's facing away?

To be fair I do have trouble completing the kill from behind. But when I am able to line things up so I'm definitely killing them while I'm behind them with plenty of time left on the stun I've employed and in the same position I use when getting from-behind kills via close combat weapons, it's far more often the case that I don't get the kill from behind and I have no idea why.

I don't know, could be a thing. I've all but given up trying to complete the 10 kills from behind with assault weapons. It is strange, I'll get 8 kills fairly easy, then spend 5 hrs on the last 2. I swear sometimes I most certainly got a back kill, but it didn't call it that. I can't compare to clisecquarters because I have seeker revoker so most of those are definitely back kills.

Gotcha. When using Surge I am able to finish this challenge with enough time to spare, so never bothered to notice if behind kills sometimes don't register. I'll try some experiments this week and let you guys know what I observe.

By the way, one non-Surge way to get behind kills with assault is to camp near a control point owned by your team and wait for bots to try and capture it. Bots often run in circles while capturing points so every now and then you'll get a kill while they're facing away from you. Takes longer because of its unreliable nature but works. Overdriver works best among the options I have.