Upfront theme just loads a blank page


I'm starting to try and use Upfront theme editor and so far am not having any joy at all. I want to start with a fresh theme and so I have generated a new child theme of Upfront using the Child Themify plugin. This has worked ok, and when going to Appearance - > customize the Upfront editor is loading no problem.

Now, all I have done so far is to add a background image. When in the editor this looks fine and I can see it, however after saving, closing the editor and visiting the site, I am greeted with a blank page.

The site is here - http://machete.wmdstudios.co.uk

Any ideas?