My non-vampire right after the Soul Cairn tries to eat my soul. She talks about becoming a vampire or being soul-trapped, but the dialog ends and won't continue.
My objectives is giving me the "Speak to Serana" twice.

I'm on the Xbox.
Disregard. A simple reload helped, though there was an odd graphical glitch (The reloading had the room illuminated like the Soul Cairn was opened, but it wasn't).