Avia Layout Builder not loading

There have been a million threads with the same topic. And I’ve read every single one of them, and tried every possible suggestion, without any solution.

My scenario: I have a multisite installation, with each of the five sites having a child theme. There are various plugins in use across the sites, some of which are network activated, and others that are activated only for specific sites. Running WordPress 4.2.2 and Enfold 3.0.5. The problem also occurred after a previous WordPress and/or Enfold theme upgrade, so we had to revert the site and perform the process again.

What specifically has been tried: disabling/deleting all plugins, upgrading Enfold via automatic and manual methods in WordPress as well as FTP, various php.ini and .htaccess adjustments, WordPress files being overwritten with a fresh copy, cloning the site to a new location, hard refresh, clearing browser cache/history/cookies, new user accounts, and more. I’ve spent about 10 hours trying to solve it so far.

A side issue is that upgrading Enfold to the latest version also manages to reset various footer widgets and other content on some of the sites, but not all. I’m not sure how/why this could happen, especially since we’re using child themes. We are using the custom.css file in the parent theme /enfold/css folder, but that’s been backed up and carefully restored manually just to be safe. It’s bizarre.