I have been using this beautiful devices for a week - it actually rebooted 3-4 times during first 4 days. No update was pushed on this device since I opened this box even though I set it up "automatic" update.
Out of frustration, I did manually check software update, and it did 2 updates [one light (around 10MB) and one heavy(around 180MB)] till I get the message of "up to date" when I checked manual software update. then the reboot are gone - at least for 3 days since updating.
so not 100% confident but check your software update
(I think the update is sourced directly from Samsung or microsoft - since I am using Rogers unlocked version with T-Mobile US)