On Windows 10 Professional, driver 16.7.3, when in desktop mode after just a few minutes the monitor goes blank but still has a video signal. The only thing to do is to turn off the power.
However, when playing a full screen game, for many hours, it's fine.
Also, on Linux / Ubuntu 16.04 LTS, my main OS, using the AMD drivers, there is no problem in desktop mode.
This problem thus is with a defect in the driver software unique to Windows in desktop mode, not a hardware problem.
Windows is not usable at this time other than for games.
Z-170 motherboard, i7-6700k, 4K DP display.
Card: RX 480 MSI Gaming X 8GB, 8-pin.
I used Intel HD530 previously for ~8 months with zero problems.