Visual Composer plugin Documentation.
Visual Composer activating creates a white screen of death
Depending on your hosting environment (e.g. shared, VPS, et cetera) and how big your database is, you might experience an issue when trying to access the Customizer. This is usually due to the Customizer timing out because of a memory limit in your server environment. The first thing you can do to remedy this is to enter the following lines in your wp-config.php file at the root of your installation:
define( ‘WP_MEMORY_LIMIT’, ‘128M’ );
Upon entering in this information everything should begin to work as expected unless your hosting provider has a limit on these parameters, which would keep them from taking effect. If your Customizer is still failing to load, the next step would be to open up a support ticket with your hosting provider and ask them to increase your PHP memory limit to a higher setting.