You may experience a problem with your Dell 4K Ultra HD monitor, which connects using the DisplayPort connection, where any open windows get resized and moved to the upper-left corner of the monitor after resuming from a sleep state from Windows 10, Windows 8(8.1) and Windows 7.
The issue has been identified with the following Dell monitor types:
Those monitors are with the maximum resolution set to 3840 x 2160 and a refresh rate of 60 Hertz. In addition, non-Dell 4K Ultra HD monitors with these specific settings and connection types experience an identical problem.
For monitors like the P2415Q (and most 4 K displays), it is not possible to change the Refresh Rate from within Windows settings.
To resolve this issue, change the monitor setting refresh rate from 60 Hertz to 30 Hertz.
The refresh rates are set in the MONITOR On-Screen Display (OSD) menu:
Figure 1: Monitor OSD Menu
The OSD Menu should have options for either MultiStream Transport (MST) or DisplayPort 1.2 (DP1.2).
Setting MST options:
Setting DP1.2 Options