They changed the game a bit. I guess they got tired of us killing scavengers with missiles. You can kill a few of them, but then they disappear. The count disappears. You have to land and kill them by hand.
I took 2 "Exterminate Scavengers from…" missions. The first one I thought was bugged because no count after killing several so I jumped out to reload and come back. Same thing happened. I took out 4 or 5 Scavs and then couldn't find any more. I landed and they swarmed my ship. Between the ship's shield, my shield (and my fantastic shooting ability) I was able to take out 4. Then I noticed upper right said 4 of 5. Suddenly my ship was being hit by someone else. Turned out to be a sharpshooter holding back. Once I killed him (no easy task) the mission finished.
Similar on the next mission; I took out a few guys from the ship and then no more showed up. I scanned with the free camera so there was no one there. Guaranteed! So I landed, this time being a bit more wary, and sure enough 5 guys came at me and the ship. I would say I'm getting better at this but there's no way I would have survived without the ship's shield!
So be prepared if you missile your way through Scavenger Missions!