I saw the trophy wolf Voref once in the Chapter 3 swamps, but ignored it as I was already carrying the wyvern head. I didnt kill or even attack it. Now I cant get the damn thing to come back. I've tried exploring the entire swamp at all times of day. In my previous playrhoughs it has always spawned near the tower/golem graveyard.
Is there a known bug with this?

Not a known bug. Voref should spawn somewhere not too far from the path between the tower and the golem's graveyard, usually between the corpses and the obelisk. But he may have wandered. Try resting at the campfire near the corpses.

The first time I saw him I was dealing with other creatures that were active in the area, and when I caught up to where he'd gone... no sign of him. Eventually I gave up, did some other things, and when I was passing through the area around the golem pylons again, there he was, starting along the same path he'd taken before.

Given that you're experiencing something similar, I get the feeling that he 'resets' in cases like this, but not necessarily right away.