VC stopped working | Internal Server Error 500

Maybe it is necessary to increase the PHP memory limit.

Open file \wp-includes\default-constants.php, find code (or something like this):

if ( !defined('WP_MEMORY_LIMIT') ) {
		if( is_multisite() ) {
			define('WP_MEMORY_LIMIT', '64M');
		} else {
			define('WP_MEMORY_LIMIT', '40M');
		}
	}

	if ( ! defined( 'WP_MAX_MEMORY_LIMIT' ) ) {
		define( 'WP_MAX_MEMORY_LIMIT', '256M' );
	}

and replace with new one:

	// set memory limits
	if ( !defined('WP_MEMORY_LIMIT') ) {
		if( is_multisite() ) {
			define('WP_MEMORY_LIMIT', '128M');
		} else {
			define('WP_MEMORY_LIMIT', '128M');
		}
	}

	if ( ! defined( 'WP_MAX_MEMORY_LIMIT' ) ) {
		define( 'WP_MAX_MEMORY_LIMIT', '512M' );
	}