Periodically on my '16 when I hit the button to turn the cruise on nothing will happen. Usually if I keep tapping the button it will eventually come on. I have heard people complain about this quite a bit and would guess either the actual button on the steering wheel or somewhere in the circuit there is a slightly loose connection (like in the clock spring). Have heard all types of different "turn the wheel this way, tap on this, etc...." and haven't really been able to figure out any regular thing that works except for just keep on tapping the button. Everytime I want cruise it's because I"m on a straight section of freeway so can't really yank the wheel back and forth, come to a stop, cycle the key, etc....
Not sure if the OP is saying that they are running down the road with cruise working and turns off itself, or simply saying it won't turn on. I've never had it just turn off by itself before and the only issue is getting the cruise on.....and not actually setting the cruise speed, just when you hit the "on" button and it shows in the display that cruise is now on and you can set it to a speed.