X - 5.2.016
Pro - 1.2.045
Cornerstone - 2.1.0
I thought it would be worth sharing, the solution to fix the Cornerstone not loading, header builder not loading. The site looks weird (I had a duplicate of icons and images in the navigation).
So how did I solve it? Follow this steps, and I hope it solves the issue for you as well.
The first thing to answer: Are you using CloudFlare? If YES continue!
- Disable any Cache or CS/JS minify plugins.
- Go to CloudFlare and switch on development mode.
- Go to Cache tab and Purge everything.
- Switch on cache plugin and purge the cache here as well.
- Disable development mode.
Did it solve your issue? I hope so, cheers! 
Update: To make sure the page builder works as they should you need to have Cloudflare development mode on.
