Brake Light On problems of the 2011 BMW X3

Tl- the contact owns a 2011 BMW X3. The contact stated while driving on the highway at approximately 65 mph, traveling in heavy rain the vehicle violently decelerated to 35 mph without warning. The contact stated that the failure was similar to slamming down on the brake pedal however, the brake lights did not illumunate during the failure. The contact stated that the vehilcle was taken to the dealer to be diagnosed but the failure could not be duplicated. The failure was recurring but only during rainy weather. The vehicle was not repaired. The approximate failure mileage was 49000. Am.