I have been having issues with using Divi Visual Builder including in the Divi theme so I deactivated and activated each plugin separately to discover which plugin is causing the issue and it turns out it is Ultimate Branding. Here is our setup in case there is something you can do to 'patch' the plugin.
Multisite (SubFolder) domain.com/_________
The Divi Visual Builder in the theme works fine on the main website, but not on any other subsite. When I deactivated Ultimate Branding (Network Deactivate), the Visual Builder works fine with the Divi theme.
I just tested out which element of Ultimate Branding is not compatible and it looks like it is:
"Global Footer Content"
When this is activated the Divi Visual Builder does not work, when it is disabled it works fine.