Interesting,
In my game I defeated all the Rusalkis in chapter 1. I’m not sure if that had anything to do with it. I visited the temple, encountered the Rusalki, and had the weedwalker shoes in the inventory of all my characters prior to attempting the quest.
I may have never encountered the last Rusalki, I’m really not entirely sure. I think you need to complete all of the encounters prior to boarding the ship. I then attempted to complete the quest in chapters 2 and 3.
I just wanted to let you know the specific circumstances that has so far resulted in the inability to complete the quest.
