Capistrano is great for deploying web applications. But the “current” symlink construction causes issues with PHP-FPM and OPcache enabled. PHP-FPM will display old pages after deployment or PHP-FPM just hangs. The hanging / freeze will result in your browser loading for minutes but you will just see a white screen.
To fix this, use $realpath_root instead of $document_root and set the SCRIPT_FILENAME in Nginx to pass to PHP-FPM.