Hi
I have the exact same issue, I collect Ariel's Bow but Kindred Judgement doesn't start. I have talked to Serana and Gelebor, exhausted their speech options, fast travelled away, come back, completed other missions, reloaded previous save points etc
Absolutely gutted as this is the last part of Dawnguard and I want to finish Skyrim......
Any word on a workaround or way for this to unlock !?
Thanks