I run mine undervolted to 1160mV at 2050Mhz which is actually the default boost clock for the Nitro+. Never had a black screen issue since day one so I reckon people who have had problems may have had other system components interfering with the 5700XT.
I've had some minor issues, but I've also had issues with my 970, 980Ti and 1080Ti, strangely enough never had any major issues with my 7970