Diagnosis
This is almost always a cable or signal integrity issue, not the panel itself. The G6 pushes a lot of data for 240Hz, and a subpar cable can't keep up.
How to Fix It
You need a certified, high-bandwidth cable. For DisplayPort, get a VESA-certified DP 1.4 cable. For HDMI, use the one that came in the box or a certified Ultra High Speed HDMI cable. Swap it out, even if your old cable 'worked' on another monitor.
If That Didn't Work
Go into the monitor's OSD (Settings > System > Refresh Rate) and try lowering the refresh rate from 240Hz to 144Hz as a test. If the flickering stops, it confirms a bandwidth limit, likely from your GPU's output port or the cable.
Heads Up
Also check if Adaptive Sync (G-Sync/FreeSync) is enabled in both the monitor OSD and your graphics control panel. Sometimes turning it off and back on can resolve sync-related blanking.