Diagnosis
That's the monitor losing sync with the signal. It's usually a cable issue, a bandwidth problem, or a feature like G-Sync/Adaptive-Sync acting up.
How to Fix It
Start with the cable. If you're using the included DisplayPort cable, ensure it's firmly clicked in at both ends. If you're using a different or longer cable, swap it for the stock one. This monitor is officially G-Sync Compatible (it has Adaptive-Sync). Go to NVIDIA Control Panel > Set up G-Sync, and try disabling G-Sync entirely as a test. If the black screens stop, you know it's related.
If That Didn't Work
The issue might be related to the monitor's power saving features. In the OSD menu, go to System Setup > ECO Mode and set it to Standard (not Off or any other setting). Also, in the same menu, set ASCR to Off. These can sometimes interfere with signal stability.
Heads Up
If you're using a high-refresh rate (like 144Hz) and your GPU is under heavy load, a low-quality cable can't handle the data rate and will drop out. Always use the certified cable that came in the box for the high-refresh connection.