After the events of the cutscene where you discover he is a Vampire I tried talking to him in the morning and the screen goes black then returns with the conversation cutting out and I cannot talk to him again about the incident. What caused this, I believe, is that I had him in my party when I returned to camp but then removed him and brought in wyll then went to sleep trigger the cutscene. I reloaded a couple times and the issue would repeat again and again. I then dismiss shadowheart and brought Astarion back into the party this fixed the problem as I went through the night scene and then was able to talk to him back in the morning without issue.