Every time I try talking to any NPC. I can not talk to any NPC.
Also, I noticed something. When talking to Sven, it is Sven who says these set of dialogues, but when talking to other NPCs, it's the player who says "Oops, you've encounters a bug...", if that means anything.
This bug first appeared when I tried talking to Sven for the first time. By then I already had the Forge quest for Sven, and a few others, in case they are the trigger.