https://bugzilla.kernel.org/show_bug.cgi?id=201067
--- Comment #1 from Nicholas Kazlauskas (nicholas.kazlauskas@amd.com) --- Created attachment 278423 --> https://bugzilla.kernel.org/attachment.cgi?id=278423&action=edit Patch that reverts the 15% reduction in set dispclk
While I can't reproduce your issue under a similar setup I think I have an idea of what the issue is.
Can you try this patch?