The second Avalon Datapad/Missive shows up and is collectable, but does not give credit towards the seasonal challenge. I can leave the Avalon mission, go to orbit, relaunch the mission, return to the location of the second datapad/missive and it's there again. I can collect it again, but it still does not credit the seasonal challenge. I am stuck at 1 of 2 for that part of the seasonal challenge.