Just a quick one, hoping it will help someone,
If you have a wordpress site with WPBakery Page Builder running on it, and find the frontend builder is not working, and if you also happen to use cloudflare – Rocket Loader™ is your issue.
Go to cloudflare and under speed –> Optimization –> turn off Rocket Loader™
Go back to WordPress and within a few mins, or the time your cache takes to update – your visual composer/WPBakery Page Builder will be working again.