I had this happen twice last night. This is what actually happens: You are killing the appropriate mobs, and you loot the item (the Sensor Array, witnessed by two other group members), however it does not advance your quest objective, it still shows that it is missing. Upon relogging it shows the quest completed but it does not advance to the next phase, forcing you to reset it instead of being able to scan the vehicles. This happened twice, once for two different characters. It's definitely buggy. The few other times I did it I had no issues whatsoever.
Please report this as a bug so it gets fixed ASAP, it cost me quite a while last night.