from https://stackoverflow.com/questions/25774999/nginx-stat-failed-13-permission-denied
Nginx operates within the directory, so if you can't cd to that directory from the nginx user then it will fail (as does the stat command in your log). Make sure the www-user can cd all the way to the /username/test/static. You can confirm that the stat will fail or succeed by running
sudo -u www-data stat /username/test/static