Re: Shut Down doesn't shut down
The issue turned out to be caused by "Do Not Disturb" rules. Even though these rules cannot be set to directly power-on the phone, their mere presence causes the side effect of booting the phone once a day. There are several pre-installed rules. After deleting all these rules the device now remains turned off indefinitely. These rules are found under Settings -> Sound & notification -> Do Not Disturb -> Automatic rules.