Unable to Save Page with WPBakery Page Builder
Sometimes this problem appears when WordPress is reaching a certain limit applied to the Apache service. So, it will require to increase that particular limit to resolve the issue.
Here is a possible solution for this issue. Add this code in the .htaccess file.
<IfModule mod_substitute.c> SubstituteMaxLineLength 10M </IfModule>
There are a few other limitations which cause such problem, and it might be server FastCGI or mod_security low settings value. Here below we are providing some recommended values. You can add these values on the provisional basis to check whether it resolves your issue or not. If this resolves your issue, you can use this code and can contact your hosting provider for further details.
Check below link for more information: