I've done a fair bit of research on this, and tried: the .htaccess trick, switching Upfront child themes, clearing the cache, using different browsers, and disabling every plugin before making changes/saving. Nothing is working.
The only clue I have is that jQuery seems to hang on the Upfront editor (and only for the editor). Everything else loads like normal on every other page, except that Upfront seems to be a sluggish theme in general.
Aside from "There was an error saving your changes", these are the jQuery messages:
I'm not clever enough to understand what's going on there, so I'm turning to you for help! Support access is granted, I am looking forward to getting this sorted. ????