Quote:With the latest Google Play services update, Android is rolling out a new security feature that automatically restarts (or auto-reboots) devices that have been “locked for 3 consecutive days.”

Under Security & Privacy, the release notes for version 25.14 of Google Play services includes:

• [Phone] With this feature, your device automatically restarts if locked for 3 consecutive days.
  

By “Phone,” that should also extend to tablets, with the other device categories — Auto, PC (Play Games Windows app), TV, and Wear — excluded. An auto-reboot occurs if you haven’t used your phone or tablet for over 72 hours.

Restarting a device, returns it to a Before First Unlock (BFU) state where data is encrypted and harder to access as you’ve yet to enter your passcode, with biometric logins not yet enabled. On Pixel devices, the bottom of the lockscreen notes how you have to “Unlock for all features and data.” In comparison, data might be easier to access After First Unlock (AFU) when you are “signed in.”

Google rolling out auto-restart security feature to Android

Android phones will mimic iPhones by automatically restarting, but it's a feature