I was driving today in my 3 with update 2018.14.13 and on two different occasions with nothing I could see to cause it the vehicle applied the brakes firmly from 75mph and then let off. The first time a big pickup was behind me and it scared the crap out of me as I did not want to be rear ended or to piss the guy off and have hime decide to try and run me off the road thinking I was doing it on purpose. He was coming up on me fast but I figured he would go around me since I was in the right lane. Probably scared him too. Luckily the second time there was no one behind me. I think Tesla needs to find a fix for this before one of us has an accident caused by this unexpected behavior. If there was a set of known conditions that trigger this we could at least try and ameliorate the behavior by disengaging AP when we saw the conditions materializing. I can't find any consistent pattern to suggest what triggers it.