Wheel sensor MUST be positive going forward and negative going backwards.
Make sure the Direction of Travel shows correctly Forward or Reverse.

Your GPS antenna (black puck) won't make any difference, that is just an antenna. The GPS receiver is built in to the Mk4.

You should try the Mk4 in another vehicle and check the speed pulse input etc to confirm if the problem lies in the nav unit or in the car.

Jochen