Wanted to chime in that both I and a friend are experiencing the same bug on this patch. I'm playing Astarion Origin with a Selunite Shadowheart, they're playing Durge with a Selunite Shadowheart. Both tactician, if that's relevant. Exact same issue as you mentioned - when she should be having her defeated dialogue with Shadowheart, Viconia instead gets stuck on the dialogue she has if you approached her pre-fight without Shadowheart. Speaking with her multiple times loops through the same tree.
I'd wondered if it was related to the state in which Viconia got knocked out - for me, she kept getting KO'd at 0 hp instead of 1 - but it seems that you're having the same problem when the game knocks her out correctly.
