This is something relatively new. I generally have my Win10 (1709/16299.371) machine set to turn the monitor off after 20 minutes' idle time... no sleep mode, just monitor-off. But concurrent with some recent update, I often wiggle the mouse to bring the screen back up, only to see that Windows is back to the sign-on screen. Of course all programs that had been running were shut down and have to be restarted also. When this happens the computer does not shut down completely, but it's as though it goes into some super-hibernate mode where the BIOS is still running but it loses Windows. This doesn't happen all the time, but I can't associate this action with anything else going on. I cancelled the monitor-off feature and everything runs fine, just that the screen is always on. Just wondered if anyone else has seen this.