https://bugs.freedesktop.org/show_bug.cgi?id=48772
--- Comment #17 from Andy Pillip andy@madspunky.net --- This is not a cable issue.
I just figured out that for me the issue only occurs on a dual screen setup.
Now I'm running the 3840 resolution on my external screen while switching off the internal one – without any issues.
Tvrtko, do you have a dual or single setup?