Unfortunately this is just one of those awful challenges that you have to accept will take a while to get, unless you get lucky. Also make sure you aren't tracking it, because tracking is apparently one of the ways it bugs and doesn't progress.
What annoys me is the first game I tried to get it, with my stinger I did have someone putting painting locks on, and hit vehicles enough to complete it.
But it bugged out.
So I have to do it again and so far I've had one person paint a vehicle once that let me hit it, and a few times where I someone painted but I got killed during lock-on.
It's annoying for sure.
I had a CQ game on Firestorm where I managed to get a few hits with the stinger to get it up by about 150 points. So I'm at around 350/1000 at the moment.
