Why I am getting 503 console errors when using the Site Studio admin interface?

This is due to a Drupal core bug.

You may see 503 console errors when using the Site Studio admin interface, if you're using translations, specific have "Account administration pages" checked in the translation settings and users have an admin language set. 

This is a Drupal core bug, which not only affects Site Studio but other modules. 

Please read this Drupal.org thread for more information and to find the relevant patch to apply.