The contact owns a 2020 Honda CR-V. The contact stated while her husband was driving 5 mph, the brakes were depressed by mitigation braking system. The contact stated no warning light was illuminated. The driver was depressing the accelerator pedal but failed to accelerate causing the vehicle behind him to rear end their vehicle. The contact stated no one was injured nor sought medical attention. A police report was not filed. The contact towed the vehicle to the local dealer but they were unable to duplicate the failure. The vehicle was not repaired and the driver deactivated the forward collision on the vehicle. The vehicle was towed to a collision shop and had the rear bumper replaced. The manufacturer has been informed of the failure. The failure mileage was 6,028.