Astarion and Cazador

Honesty probably already know, but doing my first play though as a moon Druid so I am constantly wild shaded, and after finishing the fight I didn’t de wild shape before opening the coffin and Astarion just talked to himself, didn’t ascend but just left my party and now I have to do the battle over again. I have done it 4 times to final beat it without him ascending mid fight and with Astarion and not I got to do it over again. Kinda annoyed.