DIAGNOSIS This is typically caused by the monitor syncing to a changing refresh rate (Adaptive-Sync) or a momentary signal loss due to cable or port issues.
FIX Navigate the OSD with the joystick. Go to Game Adjust > Adaptive-Sync. Toggle it to Off. Test if the black screens stop. If they do, the issue is related to G-Sync or FreeSync handshaking. You can try re-enabling it later with a different setting. Next, check your cable. For high refresh rates at QHD, you must use a high-quality DisplayPort 1.4 cable that came with the monitor or a certified replacement. Reseat the cable at both ends.
IF THAT DIDN'T WORK The issue could be GPU driver related or a power saving feature. Update your GPU drivers to the latest stable version. In the NVIDIA Control Panel (for NVIDIA GPUs), under "Manage 3D settings," set "Monitor Technology" to "Fixed Refresh" temporarily to test. In the monitor OSD, navigate to General > HDMI Compatibility Mode and ensure it is set to 1.4 (not 2.0) if you are using an HDMI cable.
HEADS UP If you are using a GPU power cable daisy-chain or an underpowered PSU, the GPU may have momentary power dips that cause signal loss. Use separate PCIe power cables for each port on high-end cards.