I recently installed 18.04. I have two Monoprice 4K monitors, however, this issue occurs with just one connected.
If I connect via DisplayPort the screen flickers constantly. I've tried three different cable brands, all 6' or under, so I'm now convinced it's not the cable. The DisplayPort cable did work without flickering in Windows. Two other Ubuntu distros demonstrated the same problem in live cd. It also shows up during installation. Toggling the power on the monitor will eventually fix it. If two montiors are connected it causes both to cycle and eventually I can even get both monitors flicker-free. This will last until the next power cycle.
I've tried the AMD proprietary drivers, but that didn't help.
I've tried upgrading the kernel to 4.18 and 4.19 RC and adding amdgpu.dc=0 to grub.
HDMI works, but is EDID limited to 30Hz for some reason.
Any other ideas?
Flicker: https://drive.google.com/file/d/1ZwTSjIKBc3pOPCP1xj2es3u4bXSdXmst/view?usp=sharing
