Try "Ultimate Windows Tweaker 4". Worked great for me and it's free.

http://www.thewindowsclub.com/ultimate-windows-tweaker-4-windows-10

Many users have solved this problem by unplugging any joystick/game controller attached. Worked for me. It's a MS bug I'm sure.

The monitor not turning off was solved by unplugging any joystick. This may have the same effect on sleep.

For what it's worth, Gary on a different forum discovered that his USB Joystick was the problem. I disconnected my Wingman Joystick now the monitor shuts off!