The fact the challenge is bugged is bad enough but hardly any targets get laser designated in games anyway.
1) Requires another player to mark a target (Outside of player control).
2) Requires you to be in range of the target, have line of sight on the target and have ammo (Somewhat within player control).
3) Relies on the laser guided projectile to actually hit (Outside of player control).
4) Requires the challenge to actually track, which in the majority of cases it doesn't do (Outside of player control).
Only 1 of 4 of those does the player have any influence over. That doesn't seem like a reasonable challenge since there's no skill involved, it's luck and what's worse, you need all those things to align multiple times.