I had a similar incident
I had a similar incident today, while driving on i580 and around a mile away from the 680 exit. I was on the left lane to the exit late and there was back to back traffic on both the lane to my right and left. There was nothing in front on my lane for at least 100 yards, and suddenly my car applied the brakes hard while in ap. I was attentive and quickly pumped my gas and took over and sped up the car to avoid the truck on the back rear ending me. I was going at around 40 and the braking slowed it to roughly 30 mph. But it was scary. I called and reported this to Tesla. They could not find anything wrong. But I don’t trust ap now. Be attentive while in ap mode