I recently purchased a second Traktor Kontrol S2, to store in a different location than my first. (I travel a lot.)
The first one works like a charm, but I'm having trouble getting the second controller to work. When I plug it in to my USB hub, it lights up for a second, but then goes dark and doesn't control Traktor Pro (3) at all. I've used multiple hubs to the same effect, so I don't think that's the problem. I'm also inclined to think the controller works fine, because it's brand new and does light up when I plug it in.