This is a real problem for me as well, for some time now, with amdgpu (Radeon
RX560), Fedora-27, gnome-shell and Dell P2715Q monitor. It happens both on Xorg
and Wayland.

> kernel: [drm:amdgpu_atombios_dp_link_train [amdgpu]] *ERROR* displayport link status failed
> kernel: [drm:amdgpu_atombios_dp_link_train [amdgpu]] *ERROR* clock recovery failed
> kernel: [drm:amdgpu_atombios_dp_link_train [amdgpu]] *ERROR* displayport link status failed
> kernel: [drm:amdgpu_atombios_dp_link_train [amdgpu]] *ERROR* clock recovery failed

The nuisance here is this almost always crashes gnome-shell. Attached coredump
excerpt.

I used to be able to circumvent the gnome-shell crash by disabling dpms ("xset
-dpms" and/or "xset dpms force off") but this doesn't seem to help anymore.