CSS/JS on the page returns 404 error on first load

It turned out to be an issue with perusio config for Nginx.

Adding this fixed the issue.

Apparently it was giving 404 to some files, forcing Advagg to then regenerate those files.

   ###
    ### advagg_css and advagg_js support
    ###
    ###
    location ~* files/advagg_(?:css|js)/ {
      gzip_static on;
      access_log  off;
      expires     max;
      add_header  ETag "";
      add_header  Cache-Control "max-age=31449600, no-transform, public";
      try_files   $uri $uri/ @drupal;
    }

Thanks for info!