I’ve done this assassination loads of times now. I’ve cancelled sprint many times, I’ve cancelled inputs many times, I’ve gone behind the elite many times. It still won’t register, personally I’m just annoyed at this point. I’m sure many others have had this issue of the challenge not registering. For such an easy and simple challenge it’s really frustrating when it doesn’t work, yes I know it was a bugged achievement in the original Halo: Reach, frankly that’s not an excuse when this challenge was specifically used.
Hey OP, to keep things tidy and save a million threads on this:
if you are on PC please see this thread:
https://www.halowaypoint.com/en-us/forums/f3681fbc78fa43878c4aec9a63a46224/topics/because-you-begged-seasonal-challenge-impossible/5f6dbd6c-1201-4b86-aa44-a27e654a78d7/posts?page=6#post111
For Xbox you can use this thread:
https://www.halowaypoint.com/en-us/forums/84ad72a8b51847978545f685f651fc15/topics/because-you-begged/a3b79f15-868b-401b-b216-58cf21abe3dd/posts?page=12#post223
Also worth reading over the latest info from 343 about the challenge:
https://www.halowaypoint.com/en-us/forums/243780d3b80b4bb6ac7917a8942286db/topics/mcc-development-flighting-updates/3e3252e1-297a-4590-a7ab-67c133b3d37d/posts?page=4#post65