Comment 21 for bug 1768610

If you want to try that, you can grab a more recent kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/ but I doubt that this will fix your issue. I'd bet on a configuration thing, but not sure what. You don't, by any chance, have a custom xorg.conf (in /etc/X11 or /usr/share/X11)? I think that working under Wayland but not Xorg is an important clue.