Hiya,
Ok so I figured out the issue. I had WPtouch Touch Mobile plugin active and this seems to be the culprit. I deactivated WP Touch and, although I lose that functionality, I can see when I toggle to the mobile view at the bottom of the customiser menu and everything is as I would expect it to be now.
Anyone else have issues using WPTouch Mobile Plugin with Storefront Theme?
Thanks for responding!
