The best explanation is watching this video
problem ocurrs when amd drivers version 18.9.3 or 18.10.2 are being used and monitor is connected through displayport.
i'm currently using 18.5.1 drivers, which shows no problem.
windows 10 x64 1803 and 1809 it's the same problem, so it's directly related to drivers
link does not work. Please describe your issue and give your full system and OS specs.