Is there any reason why you don't use a displayport 1.2 connection and run your display at 3840x2160 @ 60HZ instead of 30? That may also inadvertatently solve your issue.
When did this start happened, after a driver update?
As there has been no update on this thread, I am locking the discussion.
If you are still experiencing the same issue, please start a new discussion and provide the essential information required by clicking this link > https://community.amd.com/thread/196209