Spoilers:

after finishing the Soul Cairn / Valerica quest, I dismissed Serana for a bit before joining up again. Since rejoining however, the only dialogue options are the standard follower ones: browse inventory, wait here, and dismissal. All of her unique dialogue options are gone. I'm on my way to the ancestor glade now, and still no unique dialogues.

Dawnguard has been a horrific mess of bugs for me, with and without the unofficial patch, so I'd like to know whether I'm missing dialogue with her. (Now that I think about it, I don't think I have a pre-dismissal backup save....). Can anyone confirm?

Some of her dialogue only appears during certain quests.

Thanks. But can you confirm that Serana has NO unique dialogue options after Soul Cairn / during Unseen Visions? She has as even fewer dialogues than the Dawnguard followers now (who I can ask why they joined).