I have noticed this a few times lately - bounties on the board in Port-a-Lucine don't actually exist. I think this affects those in the Quartier Marchand. Tonight there was the 'axe murderer' and the one that 'prowls the Widow's Walk' listed, but neither NPC was present at all. I checked the nodes where they usually spawn, and every nook in the rest of the district, too. They had not been killed already, as the area initialized as I entered it and it was only 8pm IG.