Hey Nate,
This file should fix that error. https://github.com/mautic/mautic/blob/e13bb002fa9107199d68e07516a11ede68aff499/app/bundles/CoreBundle/EventListener/ConfigSubscriber.php
As for mandrill, I’m not really for sure what is going on. Do you think you could try some debugging? The code I added to check a connection is at https://github.com/mautic/mautic/blob/e13bb002fa9107199d68e07516a11ede68aff499/app/bundles/CoreBundle/Controller/AjaxController.php#L548. The class that sets the mandrill details is in MandrillTransport.
Thanks!
Alan