I think this is/was either a bug in the radeon driver, or a faulty graphics card. (however, it was only triggered when on the lightdm gtk greeter screen). I've replaced my card with another one, and no longer have this issue.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1543782 Title: Complete system freeze some time after lock screen starts To manage notifications about this bug go to: https://bugs.launchpad.net/lightdm-gtk-greeter/+bug/1543782/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
