Active safety systems which monitor the road and have the ability to engage the brakes or steering are not infallible, and can be affected by how light is hitting the windscreen, whether this is shadows, bright lights or debris on the windscreen, although thankfully these instances are relatively rare. However, under the circumstances we would recommend that the vehicle is returned to the dealer so that the system can be inspected and recallibrated if necessary, which will hopefully minimise the likelihood of this happening again. As an owner, it is a sensible precaution to ensure areas of the windscreen and front grille that contain sensors are kept as clean as possible - use of a rain repellant product can also reduce the impact of wet weather on windscreen visibility.