If Visual Composer won’t load in the back end when you try to edit some page, please first make sure that you are using latest theme version with latest Visual Composer.
SOLUTION IS SIMPLE:
Add following line to WordPress .htaccess file:
You can put this line at the end of the file, after the # END WordPress line:
The problem is with GoDaddy hosting plans and also with few SiteGround hosting users, and problem is hosting related and it is due to mod_security check when some robust and feature rich themes from Theme Forest is used (SiteGround first encountered this with Avada theme).
hope that helps. If it did send me a paypal donation to: firstname.lastname@example.org