I am also having this problem.
Tarquin is just wandering around in front of the graveyard even after being handed both pieces of the blade.
Also, Gareth just kind of vanished off to somewhere after I finished his parent's quest, and Malady notes that both are still missing from the boat
I didn't have this problem on my first playthrough.
What are the similarities between people having this issue? For example, the save file I am currently playing on where Tarquin/Gareth are broken was created before the patch hit, and also before I got to act 2.
Whereas the the save file I didn't have any problems with Tarquin/Gareth was created before the patch.
Are people who have started brand new campaigns since the patch running into this problem? Or is it just people who had campaigns already made when the patch hit?
