Upfront Editor not loading

I’m using Upfront Spirit theme, and I can no longer get the Upfront editor to load. I’ve deactivated plugins with no luck, and I’ve confirmed that PHP 5.4 is installed server side. However, I have not updated the themes in a while for fear of potential conflict with a quiz plugin I’m using – everything on the front end is working perfectly. Is the editor issue because I haven’t installed the latest theme update?