I was driving Eastbound on highway 150 on my way to work. I have adaptive cruise control in my truck and have used it many times before on this exact road with no issues. Traffic was moving slow and the adaptive cruise control was following the car in front of me exactly how it is designed to do (ACC can be turned on at speeds as low as 5 mph in this vehicle and can come to a complete stop and restart movement from a complete stop). I drove through a section of this road right after the lake crossing where the morning sun was pretty bright directly facing us for a few seconds. During this time my foot was off of the accelerator and brake as instructed by the vehicle manual for safe operation of the ACC system. In these few seconds the truck unexpectedly accelerated aggressively with no warning and before I had a chance to react the truck rear ended another vehicle, pushing it into the car in front of them as well. I have been found liable so far by insurance. I am trying to argue on my behalf. I firmly believe I am not personally liable for this accident. The system in the truck is supposed to fail safe (meaning when meeting uncertain variables, such as low camera visibility, the vehicle should disengage the ACC instead of aggressively accelerating with no information of what is in front of it) and it did not in this circumstance. As stated, I had no input to the accelerator or the brake at the time of the accident according to the owners manual safe operation of this system