Just bought my system brand new from HP in November 2016. Running also brand new dual 4K displays (LG 27UD68-W) via Display Ports in 60Hz, using Intel HD 530 graphics with the latest drivers from HP.
After the system recovers from sleep mode (and sometimes after hibernation), one of the 2 screens displays "chopped" graphic areas. The Intel graphics properties interface (right click on desktop > graphics properties) shows that both monitors' display frequency has been changed to 59 Hz instead of 60 Hz (which is the recommended frequency of the two identical monitors). Once I change the setting from 59 back to 60 Hz, normal (and not "choppy") display is restored.
I have tried to research the issue on the internet. While it appears to be a somewhat known issue, there doesn't seem to be a working solution available.
Even though the problem does not happen all the time, it occurs frequently enough to be annoying, especially since it is compounded by another display issue about which I have posted another message on the HP Discussion Boards (re: open windows shrink and move to top left corner after sleep in Win 7).
Any assistance you can provide would be greatly appreciated!