

That is except for Serana, which recognizes me as a vampire and doesn't give me the conversation option to turn me back into a Vampire Lord. Like what happened in your case, Lord Harkon and his court won't recognize me as a vampire. Clearly, something must have messed up when the Companions turned me into a werewolf. While at the same time, I also have the ability to turn into a Werewolf (Beast Form) and have the Werewolf 'Resist Disease 100%' ability (yes, I had two Resist Disease 100% abilities), making me some sort of messed-up Vampire-Werewolf hybrid. I had none of the Vampire's abilities and weaknesses, except Resist Disease 100% and I still have the ability to turn into a Vampire Lord.

In my case, it is because the Companions turned me into a Werewolf from being a Vampire Lord. I experienced a similar issue and have been able to fix it. Background info on how I came upon my solution: (If it's TLDR, just skip directly to the solution further below.)
