Volkswagen Polo 2013: Wiper skipping and shuddering

It's usually because the wiper blades are not flipping over as they change direction at the end of the stroke, so they're effectively travelling at the wrong angle to the screen. Check the arms to see if there is a reason they are not flipping over. Did you use VW blades when you replaced them? If not try the factory blades. You could also try cleaning the screen and then using something like Rain-X.