Don't mean to necro too much, but since this is the top search result, I wanted to add my experience and resolution of this bug. I had married Hert (using some console command trickery) and in doing so I was added to her half-moon mill faction. Now if you know anything about this faction is that since Hert is a vampire, The Unofficial Skyrim Patch(In my case it's the SSE Variant) goes ahead and makes the half moon mill faction an ally of the vampires... And since I was in that faction and that faction was an ally of the vampires, vampires would simply refuse to attack me. So, you don't necessarily have to be in a vampire faction, you can be in a vampire friendly faction to get this bug. For correct resolution of this bug, check what factions are allies of the vampire factions in your game and load order (with SSEedit) and check if you're by chance in any of those factions in your game. Cheers!