To make those 20 headshots it took me more than 15 matches. Most of the matches had no headshots at all. I hit the head 1, 2, 3 times, but when I hit the shoulder and make the kill it with that shoulder-hit then it's not counting as headshot anymore? This is so frustrating.

https://steamcommunity.com/sharedfiles/filedetails/?id=3774504636
But somehow opponents seem to have no problems to give me instant 3 to 4 headshots in less than 10 milliseconds from a distance of more than 70+ meters. The game constantly makes you feel like you're the biggest loser on the planet...

Besides the headshot issue, I think this game suffers from the fact that most of the time you see (or think) you were killed in one or two shots, when in reality it was several. Most of the time, people assume it was a 1v1, when in reality if you die that fast, it was probably two or more enemies shooting at you, but you just can't see them. It would be great to be able to distinguish them from the rest—not just as enemies, but specifically the ones who actually shot at you. It is shown on the HUD, but it's just not clear enough to tell in most situations.

Go into casual breakthrough for challenges like that

U may try snipe some bots in casual breakthrough to finish the challenges.
That Instantly get killed is related to the netcode issue. Some says at killer's view, victims just come out from cover, do nothing then get killed.
DICE said theyre still working on it. Hell knows when it can get fixed.

Besides the headshot issue, I think this game suffers from the fact that most of the time you see (or think) you were killed in one or two shots, when in reality it was several. Most of the time, people assume it was a 1v1, when in reality if you die that fast, it was probably two or more enemies shooting at you, but you just can't see them. It would be great to be able to distinguish them from the rest—not just as enemies, but specifically the ones who actually shot at you. It is shown on the HUD, but it's just not clear enough to tell in most situations.
Yeah most of the time I hear that the opponent hit me with multiple headshots-hits in less than 10 ms and sometimes I don't hear anything it's just instant death. I also notices that most of the time opponents seems to see me first before I can see them. This game is really frustrating. Most stupid thing is if you hear that you made a headshot, but the game is not counting it, because I guess the last hit or maybe the first hit was not a headshot???
Do all hits need to be into the head to make it count as a headshot? And by the way: how ridiculous is it that you need more than 1 headshot hit to kill an opponent?

Go into casual breakthrough for challenges like that
Breakthrough and Rush are even more stressful than Domination (which I play to do those challenges). I only play Rush if there is a "5 revives in one life" challenge, because in Domination it's nearly impossible to complete this challenge.

Just use a sniper on casual breakthorugh. There're plenty of angles where the bots will just line up and let you pop them like pimples.