NHTSA Complaint #11663205 — 2016 VOLVO XC90

The back door, or liftgate, closes automatically (without me pressing the close button). This is inconsistent, as it doesn't happen all the time. Each time the car has been off, and maybe it's on some kind of timer. It's happened 3 times, at random, where each time it caught me off guard. One time it hit me on the back of the head. The next time my kids were sitting in the back and I had to yell for them to tuck their legs inside. The third time, was just last week, and I had to run out from under it. There is no beeping or warning, and I'm afraid it's only a matter of time before it causes serious injury. I've had this vehicle for about 12 months, and it's only happened 3 times, but I can't figure out what the causes it.