problem because of this commit
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.18.y&id=d9ef158adf04b81772a7e9d682a054614ebac2fd
discussion on Ubuntu was here
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-amdgpu/+bug/1813701