Could you install the debug binary asui dd;asui id as root, reproduce the problem and then send me the log file in /root/asui-*? After you have reproduced the problem type asui r as root to restore the release binary. And play around with the power button, different combos of short and long taps and something might eventually cause it to shutdown. Also try setting the secondary unlock key to 'none'. Something is different on your device and we just need to find out what that is. Do you have ssh? It might be a good idea to install it on your device so you can reboot it via ssh while conducting these tests.