The contact owns a 2021 BMW X5. The contact stated that while stopped at a traffic light, the Auto START/STOP feature activated and the engine was turned off; however, when the light turned green, the contact depressed the accelerator pedal, but the vehicle failed to restart as designed. The contact stated that an unknown warning light illuminated but then went off. The contact stated that several attempts were needed to start the vehicle. The vehicle was not diagnosed or repaired by an independent mechanic or the dealer. The dealer was made aware of the failure and the contact was provided a fee for a diagnostic test. The manufacturer was made aware of the failure but provided no assistance. The contact was advised to contact the NHTSA Hotline to report the failure. The failure mileage was approximately 80,200.