I have been having this issue since i purchased the card. On almost every game I encounter frequent black screens that will last for a second or so and then go back to normal. No error messages, just the brief black screen every 30-45 seconds. It only happens when in full screen mode on 3440 x 1440 21:9. If I play in windowed mode at that resolution it is fine.I have run through the common trouble shooting suggestions on these forums (turning off hardware acceleration/disabling enhanced sync/disabling freesync/disabling XMP etc.) and nothing. It has been happening on multiple different drivers. I also just changed out my motherboard and CPU and it is still happening.
Close to giving up and just RMAing the card.
GPU: XFX RX5700XT THICC III Ultra
OS: Windows 10
Driver Version: 20.4.2
Display Devices: Sceptre C 35 3440 x 1440 100hz freesync
Motherboard: Aorus Z390 Pro Bios Version: F11
CPU: I7 9700KF
PSU: Thermaltake 700W
RAM; 16GB 3200 MHZ