Has Astarion been in your active party at any point? If he's recruited but just told to wait at camp and was never part of the adventuring party then he probably won't show in that button until you join him to the active group and then leave him in camp. I had a similar issue right after the patch dropped with a different companion who was in my camp but had not yet ever been in the party with me. Once I put them in the party and later left them at camp, they then consistently appeared under that button when not in the party. I have yet to see someone who has been an active companion fail to show up there.
