DIAGNOSIS This is a handshake issue between the monitor's power saving features and the PC's sleep state, often related to the DisplayPort version.
FIX First, update your GPU drivers. Then, enter the monitor OSD via the joystick. Go to System Setup > Power Indicator and set it to On. This can sometimes resolve the handshake. Next, go to System Setup > Power Saving and set it to Off. This prevents the monitor from entering a deeper sleep than the PC.
IF THAT DIDN'T WORK The issue is likely with the DisplayPort link training. Replace your DisplayPort cable with a certified VESA DP 1.4 cable. If using HDMI, try a Premium High Speed HDMI cable.
HEADS UP When the monitor fails to wake, first try pressing the Windows key + Ctrl + Shift + B to reset your graphics driver. This often restores the signal without a hard power cycle.