I am seeing different HDMI and monitor issues since upgrading from a 5th gen NUC. In summary:
1) The NUC6i7KYK, when trying to put the HDMI monitor in sleep mode (Windows 10 Power Settings, turn off monitor after xx Minutes), instead just cuts it off, leaving the monitor to believe it has been unplugged. This is inconsistent behavior when compared with my two previous NUCs. This causes the 'Monitor Unplugged' message to float around the screen until the monitor itself decides to go to sleep on its own.
2) The same above behavior occurs when the NUC is completely powered off. An older 5th gen NUC, when powered off, correctly puts the HDMI monitior in sleep mode immediately. The new NUC6i7KYK, when off, makes the monitor think it is not plugged in at all.
My only conclusion here is that there seems to be a problem with the cable detection scheme, the HDMI hot plug detect signal, and/or its handling inside the NUC6i7KYK.
When I try to wake up the monitor after it has put the monitor to sleep (by wiggling the mouse), I get these behaviors:
3) Using Driver GFX_Win7_8.1_10_64_126.96.36.19901_KY - If i leave a window up, say a browser for example, upon waking up it displays the browser window (the foreground app) surrounded by a complete black screen, no taskbar, no background image, no desktop. I cannot see the mouse's cursor and the display is frozen. I have to unplug the monitor and plug it back in, then it self-corrects.
4) Using Driver <hmmm - the previous one - seems to no longer be on the website...> - If I leave a window up, again, like a browser, upon waking up the monitor, the window has been re-positioned and re-sized down to fit 1280x720 (the lower resolution windows default). But my monitor is always in 1920x1080 resolution mode - I believe this is a side-effect of Windows "losing" the monitor, and then scaling the active content to its lower resolution default, "no monitor attached" settings. Upon waking up the monitor, the open app or apps have all been jerked around and pushed to the upper left corner of the screen.
Looking for advice on any or all the above. In some ways they all seem related, and they are all quite different than the behavior exhibited by my previous 5th gen NUC systems using the exact same monitor and the exact same OS (Win 10 Pro, 1607). Monitor is a Dell ST2420L using the HDMI input connector.