This problem was apparently caused by the combination of running Ubuntu in Virtualbox and trying to apply GUI settings (either through Tweak Tool or the System Settings > Appearance panel) with a dual screen setup. After closing my laptop screen this started working.
This problem was apparently caused by the combination of running Ubuntu in Virtualbox and trying to apply GUI settings (either through Tweak Tool or the System Settings > Appearance panel) with a dual screen setup. After closing my laptop screen this started working.