Further debugging, I discovered that the screen blanking issue was being caused by a faulty power supply on the DisplayPort Expander/Splitter, it kept resetting. This was causing the errors.
** Changed in: xorg (Ubuntu) Status: Incomplete => Invalid -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg in Ubuntu. https://bugs.launchpad.net/bugs/1531422 Title: i915 underrun errors causing screen blanking To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1531422/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp