When you click the edit button to update your Default credentials, you may be taken to a page that is missing the credentials fields and you will see a brief prompt regarding a 404 error.
To resolve the error go back to the LOCKER list and click the red "X" for the "Default" locker. Once the locker is removed, go back to your dashboard and launch the web app. You will get prompted to enter your credentials again.
If you are still having any issues please submit a support ticket.