Looks like your nginx config file like this?

server {
    listen       80;
    server_name  example.org;
    return       301 http://www.example.org$request_uri;
}

server {
    listen       80;
    server_name  www.example.org;
    ...
}

Setting the error_log /var/log/nginx/error.log debug; and show us what the log...