Have a reoccurring problem with my R9 270x VGA card with my LG 27UD58-B Monitor. If I shutdown the monitor or it goes to sleep mode, after wake up the VGA does not support 3840x2160@60hz and switch back to 3840x2160@30hz. There are two solutions to get it back:
#1 I restart the whole system and then I can choose 3840x2160@60hz in the VGA adapter modes
#2 I turn off and on the DP 1.2 mode in my monitor OSD menu. After that the 3840x2160@60hz is visible in the VGA adapter modes.
If I turn my monitor off for several minute, the windows disconnects my monitor and switch to Generic not pnp monitor. After that I have only 640x480 resolution (as headless with TeamViewer). If I turn the my monitor on again he "finds" the device again.
I use Delock Premium Display Port cable 2m. I have the same issue with the original Display Port cable from the LG.
My system is Windows 10 x64.
Crimson driver version 17.4.1