2023 Subaru Outback forward collision avoidance problems

My son was traveling at an appropriate highway speed when the truck in front of him stopped suddenly. He braked immediately and was able to slow down significantly, but not enough to avoid colliding with the back of the truck in front of him. He was going approximately 20 mph, still braking, when the collision occurred. His best recollection is that the vehicle's pre-collision system did not engage until after he collided with the truck. There was damage to the front end of the vehicle but it was not severe.

The contact owns a 2023 Subaru Outback. The contact stated while driving 35 MPH and coming to a green light with no vehicles nearby, the Eyesight Driver Assist camera malfunctioned and the vehicle came to an abrupt stop. The Collision Prevention braking system activated with the warning light displayed on the instrument panel. The contact immediately deactivated the fuel saving button and depressed the accelerator pedal for the vehicle to respond.