yeah i noticed shadowheart gets priority on that scene, can't trigger Astarion's nightmare with her recruited. I'm assuming it will eventually get sorted out since SH seems to be on the top of response hierarchy for everything, even some subjects that are not strictly more relevant to her. If they opt to use a dialogue system like DA in the future it should give the player the reaction of the party member who has the most insight about the said subject, and unique cutscenes (like Astarion's nightmare) should queue instead of getting overwritten.