Thought I had a problem on my NUC6i3SYH waking up from sleep. The NUC seemed to activate after a mouse/keyboard press, but the screen remained black. Had to press a button on the monitor to turn it on. This would only happen after not using it for a few hours. I have a 21.5" Samsung from 2015 connected over HDMI.
Well, turns out there is an Off Timer in the monitor settings and it was set to 4 hours by default. Can be set to Off or 1-23 hours. So the monitor turned itself off, and the NUC cannot turn it on in this state, monitor button has to be pressed AFAIK. Quite obvious once I realized it :-) Set it to 23 hours, so now the screen will wake up together with the NUC, with a single keypress on the mouse/keyboard, as long as I use it daily.
Just letting you know.