flask-login has been updated and changed it's API. Our code was updated accordingly in 9a26e165 and fe44ca89. It was changed back to the old form in 2a053b57.
For the API see: https://flask-login.readthedocs.org/en/latest/#your-user-class
To enable design management, you'll need to meet the requirements. If you need help, reach out to our support team for assistance.