I have the same issue since I moved to 10 :-(

I have had this issue since Win 8.1. Rebooting the machine fixes it as far as I can tell. 

Sleep issues in Win 10 manifest across multiple platforms, not just custom/EVGA. Usually, I've learned that power options in win 10 are more user-specific than machine-specific. Try recreating a brand new LOCAL (non-online) account and test.
 
My problem currently is that it takes around 20-30 seconds to reach a halt state from the moment I manually initiate the sleep command. I have 2 x 1 TB HDDs in RAID 1 and an Intel SSD, but that's irrelevant to the issue as it was happening before I built the RAID. Here is a rough sequence of what's happening:
 
1. Press Sleep button;
2. Monitor goes dark as normal;
3. Can hear HDDs slowing down to a stop;
4. Immediately after, just as if something is "calling" them, the HDDs initialize again until platters reach operational velocity;
5. Sits around 10-15 seconds with intermittent HDD activity and then halts abruptly.
 
Can anyone make sense of that? Where to start? :)
 

Sounds like the memory contents are being cached to the swap file before lights out. Shouldn't have to do that with as much memory as you have.