Upfront Builder not working


I’ve just turned my laptop off after spending a few frustrating hours looking around and installing plugins when I realised the reason I cancelled before. The Upfront Builder doesn’t work. I’ve tried the Fixer theme and the Scribe theme, exactly the same thing happens. I even tried creating a new theme and that doesn’t work at all. I’ve uninstalled plugins and reinstalled them but still the same thing.

Pressing Upfront on the homepage seems to break the page, maybe something to do with the stylesheet. It doesn’t load the builder at all. Then when I click on another part of the site (eg the dashboard) it attempts to load the Builder but usually hangs on 19% loading. I’ve managed to get access to it once, somehow, but it still didn’t function correctly.

Any suggestions what could be causing it?