I start to see the pattern about this bug now, it’s seem to tied to Krystenex’s spell being the last cast or not.
If he cast, kill all enemies, and also get an extra turn, that might cause the whole board to freeze. The only way out is casting other spell that doesn’t gain an extra turn to continue, then victory scene will trigger. But from you, even this will still cause Pet Gnome to bug, which is very bad.
So… the way to avoid this bug for now until it’s fixed is to not cast Krystenex as a finishing move.