The U2718Q monitor may show screen flicker when it is set to the 2560x1440 resolution when using an HDMI cable and RBG is the color format.
No cause information.
The current workaround for this issue is to set the color format option to YPbPr. The color format option is in the On Screen Display (OSD) menu of the monitor (Figure 1).
Figure 1
The best solution for this issue is to perform a factory reset of the monitor settings in the Others option in the OSD.