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.
Try rolling back to Crimson 16.7.1. If that doesn't work install and run Clockblocker to keep the gpu from going to its lowest power state. From what I am hearing you are right, this is a driver problem.