I have one main mission which I can't do, which is to gain Yaevinn's trust, since I already did the mission where the Scoiatel attack Vivaldi's bank. After talking to Yaevinn and telling him that I don't kill humans, he ran away, I got to the elven ruins in the sewers of the city and there the mission ended saying that Yaevinn had escaped. Since then I don't know what to do, since I don't see any more main quests.

And as for side quests, I only have one left that I can't finish either as it asks me to talk to Leuvaarden and complete the contract, it tells me he's in the dyke, but he's actually upstairs on the floor of the New Narakort Inn... When I get there and try to talk to him there is no dialogue available to finish the contract with him.

PS: I'm trying to attach an image but for some reason it doesn't work...

Strange.

It's hard to give you qualified advice without looking at Geralt's journal. Upload your current save and post the link; I will take a look at it.

It's solved, in the end I had to go and talk to Siegfried, then the story continued. I don't know why the game didn't tell me to talk to Siegfried again.