I recently added wpforo plugin and I am using Divi builder as well.
I am able to add the [wpforo] into the builder and the builder shows correctly.
However, when I load the normal page, the menu is not loading correctly.
Showing only basic links in a bullet point style.
I'm sorry but this is totally crashed. i'd recommend not use builder for forum page. The forum page should be a simple page, just edit it and put the shortocde in the main content. I'd also recommend to contact to support. The problem comes from Divi builder not from wpForo, so they should help you for sure: https://www.elegantthemes.com/forum/