You must clear all Luxon scouting parties without leaving the area, otherwise the quest will reset. When you approach the quest markers on your map, several Luxons will appear, if they are not there already. You actually only need to kill the Luxon Scout. Once that happens, the quest will update and show the next area. Often the Luxon groups spawn near large groups of Dredge and Wardens, making this quest quite difficult. In this case, you can use hit-and-run tactics -- kill the Luxon Scout and then retreat.