The quest broke early on for me where my knight said something about build up settlement, build walls, and reach baron rank. I reached the rank of duke, had all paths into the city walled, destroyed the trebuchets, and was attacked by the enemy. The quest never cleared.

Workaround: take the enemy's outpost in the southeast of the map to trigger victory. Sadly, the end game dialogs are broken too but at least you can move on.