Since creators update on april 10th monitors don't go to sleep mode on any recent drivers (16.6 works fine). There has been 3 or 4 driver updates and these pretty major issue hasn't been neither fixed nor acknowledged. Please look into it.
Click the star in Radeon Settings and report the issue. If it is reproducible, AMD will look into it.
All I see is the ability to rate it.
That's what I get for not updating my drivers.
Lol...I'm using the 16.11.5