This has happened to me twice now, it seems to be pattern. I hear the Rube music, and the local activity window says The Rube is here to trade with you. (Yay!) But then he is nowhere to be seen. He doesn't come anywhere near me and I don't see him anywhere on the street. After a while the music stops and I've missed my chance. I used to see him just fine and talk to him no problem, so that's what makes me think this is a bug...