Assault Challenge 2

I have everything complete for the Assault Challenge part 2 except for 1 flashbang kill, but I have gotten a flashbang kill 4 times now and they are not counting! I even saw it say something like "flashbang kill" on my screen but it didnt count! I thought the tracking issues were fixed with the new update? Its bad enough how absolutely hard these challenges are, now not only are they hard AF but they stop working too? Plus a suggestion. Flashbangs take waaaay too long to explode. Need to cut the time down by at least 25% if not 50%. It has made this challenge waaaaaay to difficult with them having such a long time to explode along with the fact they light up like a flashlight before they even explode.