https://bugs.freedesktop.org/show_bug.cgi?id=99801

--- Comment #12 from Harry Wentland harry.wentland@amd.com --- We're currently debugging an issue that looks very similar, if not the same. It's also with a 5k display with two DP input but on a different platform. The display pipe driving one half of the display is underflowing. Hope we'll find a fix soon.

Not sure about the issue in 4k mode but there's a good chance the display pipe is underflowing for the same reason as the problem in 5k mode.