Diagnosis
That's a classic sign of the monitor re-syncing to the signal, often triggered by a brief interruption or instability. The most common culprit for this on high-refresh-rate monitors is an issue with Adaptive Sync (AMD FreeSync).
How to Fix It
Let's start with the sync settings. 1) On the monitor, open the OSD with the joystick. 2) Navigate to the Gaming menu. 3) Find the setting for 'AMD FreeSync'. Try turning it Off. 4) Play your game for a while and see if the black screens stop. If they do, you've found the cause. You can try turning it back on later and adjusting other settings.
If That Didn't Work
The next suspect is the cable. A marginal cable can cause tiny signal drops that trigger the black screen. Swap out your DisplayPort or HDMI cable for a certified high-speed one. Also, check your graphics card drivers. Use a tool like DDU (Display Driver Uninstaller) to do a clean reinstall of the latest drivers, as corrupted drivers can cause sync issues.
Heads Up
If you're using an Nvidia graphics card with FreeSync (officially called 'G-Sync Compatible'), ensure you have it enabled in the Nvidia Control Panel under 'Set up G-Sync'. Sometimes the handshake between Nvidia and a FreeSync monitor can be finicky, especially in borderless windowed mode. Try running your game in fullscreen exclusive mode as a test.