Diagnosis
This is the monitor's built-in power-saving feature activating incorrectly due to a faulty signal detection handshake. It misinterprets a steady input as no signal.
How to Fix It
Navigate to the monitor's OnScreen Control menu. Go to General > Energy Saving and turn the setting to Off. Disable any Eco Mode or Screen Off timers in the same menu. For a connected Mac, also go to System Settings > Displays > Advanced and turn off "Allow display to sleep."
If That Didn't Work
The issue may be a failing or low-quality DisplayPort cable. Replace the cable with a certified VESA DisplayPort 1.4 cable. If using the USB-C connection, try a different, high-bandwidth USB-C cable capable of video and power delivery.
Heads Up
This issue is almost always the monitor's software, not the computer's graphics driver. Updating the monitor's firmware requires a Windows PC and the LG OnScreen Control application.