I have same issue, but i can provide some additional information =)
Such as this screenshot of the MSI Afterburner log taken after playing CS:GO with minimal settings. Software was installed few minutes ago.
I have tried 3 versions of radeon adrenaline driver and now it is latest 19.2.1 version installed (Previous versions were uninstalled with amdcleanuputility-x64). My config: Intel(R) Core(TM) i5-2310 CPU @ 2.90GHz, Radeon RX 560 Series, Mboard - H61M-P23 (B3), with 8Gb RAM (2x4Gb), Windows 10 x64(10.0.17134.471). I have 2 monitors (one of them is TV), but i playwith 1st one only. Disconnecting 2nd one was also been tried with no success in issue fixing.
How can i utilize my new radeon videocard? My previous nvidia 560ti provided me the comparable level of perfomance in CS:GO been released 8 years ago.