+1 I faced the same bug and I cannot progress further in the game. Ubi please fix it.
Waited for the latest update to continue playing but the patch doesn't contain fix for this particular issue.
I already finished with all other provinces, but I like the game and want to finish it.
Birstan and his stupid dog are stuck near the swamps, and they are just standing there doing nothing. I tried to push him to the middle of the swamp and than back to his dog(stupid), he killed a few boars but progress bar for killing boars didn't appear.
I think in my case the thing that broke the quest was the npc patrol that spawned on the road near the swamp. Birstan started fighting with them and that could have broke the behavior tree.