I've run into a similar issue with Radeon Relive and screenshots.
Some screenshots come out great. Some just come out black screen while others come out very tiny and you can't expand the picture without severely degrading its detail.
In all these instances I ran the exact same resolution and refresh rate.
Don't know what causes the issue but with the problems I've experienced with windows 10 interfering with AMD software it wouldn't surprise me if MicroSoft is the culprit.