I am using a DELL S2718HN/NX monitor connected on HDMI port, but I had similar issues with another brand as well.
If I select in Power Options (Windows 10) the computer to go to Sleep in say 10 minutes when idle, everything works fine. It goes to sleep and when I press a key it turns back on just fine.
However, I do not want the NUC to go to sleep, just to turn off the monitor (because I use it as media server and I need it on). So I change the configuration to Sleep: Never, Turn display off: 10 minutes.
Now the problem issues: Display is turning off, but when I press a key it does NOT turn on. Everything else is working, but the display is off. I can connect to the NUC with TeamViewer and see the desktop.
From TeamViewer I can put the NUC to sleep and then, when I press a key the monitor turns on fine. Sleep works ok, but display off does not.
What I have noticed by looking into the Device Manager (with team viewer) while the display was off, is that at the moment I press a key to wake up the monitor, the monitor driver switches from PnP Generic Monitor to Non-PnP Generic Monitor, and the monitor remains off.
As stated above, if from this state I put it to Sleep and then press a key, it turns back to PnP Generic and monitor turns on. I have also tried DELL's monitor driver as well but it behaves the same.
Any ideea anyone?