I have two 24-inch displays. Its really nice to have them turn off (low power mode) when I have not been active on the computer. Sometimes they don't turn off after the time setting, 3 min, 5 min, whatever. It appears that some system program that is running is causing the problem as I have turned off all the programs that I interact with. The reason I think it may be a system program is that last night I turned off the monitor power switches long after the automatic time setting minutes had passed. This morning the displays were off when I turned the power back on, so at some later time the automatic off had worked.

As you might expect this has only been happening since the Anniversary Update as the automatic display off has worked properly for over a year on this new Win 10 computer.