did you try and install any AMD drivers?, please see this link first and stick with the on-board drivers for now until such times as AMD drivers become available:
Have you run a full system update?:
As your kernel is from June, how do you have a higher kernel than me when I just did the most recent updates?.
Linux fred2 4.4.0-31-generic #50-Ubuntu SMP Wed Jul 13 00:07:12 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux