The contact owns a 2021 Buick Encore GX. The contact stated while driving at approximately 35 MPH, the brake pedal was lightly depressed and the vehicle unintentionally came to an instant stop; the vehicle then began to shudder. The contact's mom was seated in the front passenger side of the vehicle and sustained a neck injury after the failure occurred. There was no one injured that was not in the vehicle. No medical attention was required. The vehicle was drivable and was driven to a dealer who did not provide a diagnosis but informed the contact that, the failure may have been occurring due to the Vacuum Module in the braking system needing to be replaced. The vehicle was repaired; however, the failure still occurred. The manufacturer was made aware of the failure. The failure mileage was approximately 2,500.