I installed 10 on three machines and one has a mind of it's own when it comes to sleeping. No matter how I set the power settings or screen savers if I get up and walk away from the machine it has gone into sleep mode when I come back. In some respects it could be a useful thing, but since I'm not choosing for this to happen, it's a problem.
I've discovered this issue predates Windows 10 and some online posters noticed something I have been able to verify in my situation. It you restart, boot up, or wake from sleep with the power button the system doesn't go to sleep after a brief period of idling. If you wake it from sleep with keyboard or mouse it does go to sleep. I think better stated would be, it returns to sleep. This discovery explains why at times I have thought the issue had somehow been resolved. Using the power button to wake up a system is an OK work around, but not ideal.