I have also had this on a couple of occasions now trying to update to 7.2.4 from 7.1.17. I cloned the server and switched our license over to do the update.
The error occurs whether I update all plug-ins first or as in this case, Porto first. The site works fine so if there is a clash between plugins it does not occur until the theme is updated.
At the backend the PHP engine has this in the trace:
NOTICE: PHP message: PHP Fatal error: Uncaught Error: Call to undefined method Vc_Base::buildShortcodesCss() in /var/www/wordpress-import/wp-content/themes/porto/inc/admin/theme_options.php:360
Stack trace:
#0 /var/www/wordpress-import/wp-includes/class-wp-hook.php(324): {closure}()
#1 /var/www/wordpress-import/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#2 /var/www/wordpress-import/wp-includes/plugin.php(517): WP_Hook->do_action()
#3 /var/www/wordpress-import/wp-settings.php(700): do_action()
#4 /var/www/wp-config.php(107): require_once(‘…’)
#5 /var/www/wordpress-import/wp-load.php(55): require_once(‘…’)
#6 /var/www/wordpress-import/wp-admin/admin.php(34): require_once(‘…’)
#7 /var/www/wordpress-import/wp-admin/index.php(10): require_once(‘…’)
#8 {main}
thrown in /var/www/wordpress-import/wp-content/themes/porto/inc/admin/theme_options.php on line 360
