I recently picked up a Samsung U28E590D and have been having problems with the monitor losing signal during game play (similar to this, albeit less frequently: AMD Fury X Blank Screen Issue - YouTube)
I've tried various driver versions and a new DP cable which no luck. The issue only occurs while gaming, full screen or borderless window doesn't seem to make a difference. The problem can be remedied by dropping screen resolution or refresh to anything lower than 4k/60Hz but that sort of defeats the purpose of dropping hundreds on a "flagship" gpu and a 4K screen.
running W10 64bit / R5 1600 / 16G DDR4
Please try updating to Crimson 17.9.3 and let me know if you are still having issues.