I have a WP7603 with ATT R10.1 firmware. I’ve seen a few times where when the radio shuts down after being on for a long period (a day or more) and I can’t turn it back on programatically, or via the CM command on the command line. I don’t get an error, it just doesn’t turn back on.
If you have Developer mode installed then “Low power mode” is by default disabled. Also “Low power mode” is disabled when you are connected to device via USB debug port.