The contact owns a 2017 GMC Yukon Denali. The contact stated that while driving on several occasions at slow speeds, the brake pedal was depressed but was stiff. The contact stated that the vehicle failed to slow down as intended. The vehicle was coasted until coming to a complete stop after each failure. The vehicle was taken to a dealer however, the failure was not duplicated. The contact believed that the failure was related to NHTSA Campaign Number: 19V645000 (Service Brakes, Hydraulic). The vehicle was not repaired. The manufacturer was not notified of the failure. The failure mileage was approximately 43,000.