I have a similar problem. I have a 4 monitor setup. Three of my monitors are all 24" ASUS 1080P, same make and model. Recently I added an LG 27UM88W UHD 4K monitor for photo and video editing. I have 2 AMD R9 Fury-X graphic cards in my system. They are not setup in a crossfire configuration (in X-Fire, the output ports are defeated on the second card). I have installed the latest AMD Crimson ReLive Edition 17.4.4 drivers. Unfortunately, the LG monitor on occasion fails to "Wake Up" from sleep, while the 3 ASUS monitors do not have this issue. I am currently running Windows 10 64-bit, and recently upgraded to the Windows 10 Creators edition. I have installed the latest drivers Crimson ReLive Edition 17.4.4. But I continue to have issue with the LG display after all monitors go dark. Anyone that may be able to suggest a workaround, or solution your sage advice would be appreciated!