NOTE: All the above harvests are abundant in the area below Grieg's Spire platform ( 619, 428, -583 ) Copy/waypoint 619.09, 428.17, -582.54, where it is safe to harvest them.
Return to Sanctus Seru [City], take the portal to 2nd floor go to ( -203, 182, 2 ) Copy/waypoint -203, 182, 1.79 (Arx Seru door), quest should update.
Equip Sanctus Seru Formal Garb and click on the entrance of Arx Seru near ( -197, 183, -1 ) Copy/waypoint -196.93, 183.22, -0.67.
Note: The game checks for the Formal Garb several feet from the door. If you wait until at the door to equip it, the zone won't be available. Back up a bit and try again. No need to remove and re-equip the gear.
Enter Sanctus Seru: Party for One [Piercing the Darkness] and sit at ( -107, 78, -5 ) Copy/waypoint -107.19, 78.12, -5.20.
Leave Sanctus Seru: Party for One [Piercing the Darkness] and return to Sanctus Seru: Fabrication Hall at ( -181, 181, 95 ) Copy/waypoint -181.19, 180.67, 95.49 to speak with Hulda Flintbraid.