This has been happening for some time now. My Xbox One will turn on randomly. Sometimes, it doesn't make the sound when it turns itself on, I just happen to notice the light on my Xbox One and Kinect are both on. Other times it does make the sound.
I do not have the "Instant On" feature enabled, nor do I have the "Keep my games & apps up to date" feature enabled.
I do use the Xbox app on Windows 10 as well as on my phone, but as far as I know, these cannot turn the console on (they can connect to the console, however it needs to be on first before they can).
What could be causing this? I have considered the Kinect possibly turning the Xbox on, but why would it? My Kinect is no longer connected to my Xbox and it still happens.
Edit One: This is still happening after numerous updates – 4 months later.
Edit Two: About 5 months later this is still going on. Do Xbox One's have some sort of Wake on LAN feature that is hidden? I'm beginning to wonder if it is attempting to download an update for the software similar to how Windows does. I've experienced something very similar with my Windows 10 PC turning itself on to download an update (but not install it until I manually restart).
Best Answer
I have had this happen to me many times now, I think it may have started when I connected some external HDDs to my Xbox for additional storage. Although that is just a theory that the HDDs might have something to do with it. My Xbox is also set to be fully turned off and no background updates.
My solution is simple yet very effective, buy a power / surge protector bar that has a switch which can turn the whole power bar on and off, ideally you want to have a power bar that has lights to indicate if it is on or off.
Next plug your Xbox in to that power bar which is dedicated to the use of your Xbox, last but not least turn the power bar on when you want to play your Xbox games, then shutdown your Xbox via the software interface when you are done playing your games and when the Xbox is fully off, turn off the power bar to kill all power to the Xbox, that way it cannot power on since the power bar will give no power to the Xbox.