There are two Bullvores in act 2! One in vergen mines and one in the underground caves, next to Henselt's camp! This bug is old but very annoying, because you loose both good xp and NEEDED loot (for some reason bullvores drop some draugir loot, too, like the armor fragment). If you save your game near the bullvore in caves, somehow die or simply reload at will, it is simply gone! And meditating will never cause it to spawn again or appear.

If this wasn't an ultra rare encounter, it wouldn't have been an issue! But on hard difficulty it can be a potential game stopper (you have to progress without act 2 dark armor); if you hadn't loot the draugir in beginning of act 2 and you missed this bullvore while on Roche's path, you cannot craft the oathbreaker's armor! And you need to wait until near the end of act 2, to confront the one in the mines, which thankfully doesn't disappear!

The specific one is bugged. But are bullvores actually bugged generally? Dropping draugir items and all...?!?

In act 2 while on little girls quest too, you fight bruxae, they are called wraiths and they actually drop wraith loot, too... So if bullvore is actually bugged, then this wouldn't be the first monster...