Creating an account and resurrecting this post (again!) to say thank you for this wonderful discussion
I had a similar issue with my laptop never going to sleep... Most of the time even the lock screen wouldn't come up unless I manually locked it. And after that, when on lock screen, it's like there was something preventing the screen from turning off... You could clearly see the screen light dim after a while, like if the monitor was soon going to turn off, and then 1 or 2 seconds after the monitor would fully light up again, like something was preventing the monitor from turning off...
I was about to go crazy on this, my laptop would stay on forever unless I manually shut it down. If it was unplugged, this was fully draining my battery down. All the power settings were correctly set. There was nothing in the wake logs. I unplugged the mouse because I suspected a vibration issue. I tried to unplug more peripherals. I uninstalled some software unsuccessfully... etc...
Then after reading many forum posts, I ended up here and saw the OP solved his problem by removing the nVidia Experience software. I did not have this software installed or any other special nVidia software except the nVidia Display Driver (in Control Panel > Programs). Gave it a try and uninstalled the nVidia Display Driver from Control Panel and bam! Problem solved! Monitor will turn off and computer goes to sleep as expected!
However now, I am running without the nVidia Display Driver in Control Panel > Programs... but everything looks fine. Is it mandatory to install the drivers nowadays or is Windows able to figure it out?