I've recently come to a bug where I can no longer progress in the Vampire Side quests.
When I ask anyone in the Volkihar Castle "What can I do?" or whatever it is, they are telling me to go to Vingalmo.
The problem is that Vingalmo is the only person that won't let me ask the "What can I do?" question, so I cannot initiate the sidequests anymore.

It's not a gamebreaking bug as I've got most of the goodies from the sidequests, although, due to this glitch, I cannot upgrade my Bloodstone Chalace anymore.