I have 75hz monitor and i cap my fps at 75 in games. After some time my gpu clock drops to 400-800 levels from stable 1071mhz. also my fps drops to 45-65 levels from stable 75. temperatures are normal. there is no cpu bottleneck. they dont increase back until i remove fps cap or alt+tab, alt+enter. its really annoying.
1XGB 2133MHz DDR4
RX 550 2 GB