(In reply to Bastian from comment #69)
> Distro/Kernel: Ubuntu 18.04.2/5.0.2
> GPU AMD:       Readon RX570 - Mesa 19.0
> Display:       Iiyama G23530HSU  75hz
> Desktop:       Gnome
> 
> video: https://www.youtube.com/watch?v=gNJ2kJ8hsHA
> 
> Have the same problem as the op. The problems started with the 4.20 Kernels.
> Had not this problem with 4.19 LTS Kernels. The flickering doesn't appear on
> wayland if I choose only 60hz. On xorg it is irrelevant how much hz I use,
> it flickers regardless. 
> 
> sudo -i
> echo "manual" >
> /sys/class/drm/card0/device/power_dpm_force_performance_level 
> echo "2" > /sys/class/drm/card0/device/pp_dpm_mclk
> 
> Fixes the flickering.

Just a quick update. After switching from HDMI to DisplayPort the issue
resolved itself for me.