Also there is an error in the log
2016/03/09 12:36:57 [error] 1257#1257: *5018 FastCGI sent in stderr: “PHP message: PHP Warning: Invalid argument supplied for foreach() in /var/www/html/wp-content/plugins/download-manager/admin/tpls/addons-list.php on line 204
PHP message: PHP Warning: Invalid argument supplied for foreach() in /var/www/html/wp-content/plugins/download-manager/admin/tpls/addons-list.php on line 211” while reading upstream, request: “GET /wp-admin/edit.php?post_type=wpdmpro&page=wpdm-addons HTTP/2.0”, upstream: “fastcgi://unix:/run/php/php7.0-fpm.sock:”, referrer: “/wp-admin/post.php?post=2478&action=edit”