Hey There!!
I had exactly the same problem and i took the car to the dealership and After 3 weeks the dealership found the issue and they said was the reverse camera, they changed , and my car never show the problem again.
I got My 2016 Mustang eco boost 2 months ago and the car just started doing the same, so i took it to the dealer and after they changed sensors, computer, battery, start button, pump in 2 weeks, the car still doing the same. Can not turn off Any idea?? Thank you guys!