I think i know what's going on with this vampire situation at the warehouse. During the reverend part absolutely avoid picking any aggressive options at crippled kate's, that way he stays alive and you can track down the real killer. When confronting hubert he'll transform pretty quickly into his katakan form so get ready watch for this red glow around his claws that means he's about to do his dash attack. Really important to keep quen up and dodge right when you see that glow starting, then hit him with igni during his recovery animation.

The warehouse fight gets intense especially when he starts teleporting around but if you stick near the support beams, you'll have better positioning to avoid his blood drain grab. Make sure you've got vampire oil applied and black blood running before you even start the fight, those few seconds make a difference when he transforms. At about half health he'll start doing this scream attack that staggers you but if you're behind cover when the animation starts you can avoid it completely while still keeping an eye on his dash patterns.

Once you take him down you'll get this nice silver sword deargdeith plus some crafting stuff, but what's really interesting is heading back to see how priscilla's doing. Good to know if you're having trouble with the timing, watching his left shoulder movement is actually more reliable than the claw glow for knowing when to dodge.

Just remember getting the true ending here means being patient with the investigation, those aggressive dialogue choices might feel right but they'll cut things short before you find out what's really going on.