Questions and answers quest bug after plague (PC)

I saved the people from the poison, but it still showed that I should give them the antidote although I clearly did. I questioned the prisoner then had him killed by the angry father. I left to meet Sir Radzig in a camp. He acted funny. He told me WAIT I have something important to tell you. Then he got on his horse which moonwalked a bit and then without moving its legs slided towards his hometown. He never said anything afterwards. My quest however shows that I should question the prisoner who is already dead. I think it might have to do with the time you have to wait until the villagers are cured by the antidote. Any fixes? Because I cant continue.

Here you see on the map is nothing although the quest is selected.
And the Quest Log says that I met Sir Ratzig and he told me to meet with the merchant.
I looked at the position where I think the merchant will be, but he wasnt there.