I'm a little late to the game here, but as @rnb5500 said, shutdown /s /t xxx, i.e. if X:\Windows\System32\shutdown.exe /s /t 0 as admin doesn't work, then the problem is not known by me. You might want to reboot into the developer's screen, then hold the power button until it shuts off - every time. That might be the only way.
1. When I have something that won't shutdown completely, an easy workaround is to initiate a restart, then use the physical power button after it reboots but before the OS loads. 2. A device driver that works on Home SKU but quits working if you upgrade to Pro? What are they smoking?
A PIA if I have to press the power button at every shutdown!! Now I using a Macro Script and that works well (for now)! I've still 8 months left with that device on Warranty! For that time, I could not start to 'play' with the OS and its drivers, or my Warranty is gone, and I wouldn't take that risk! After the Warranty is over, I could simply do what I like too! And that will be the time to first to change to Pro!
That's the exact same command I use in my Macro Script right now for to of the device, and it works well (for now)! Let see, if it does after the next OS Upgharde?!