Ember-Simple-Auth customised Devise Authenticator serverTokenEndpoint defaulting to users/sign_in

Pretty much as described in the title. I have a basic Ember Simple Auth setup. With a Devise Authenticator I've setup a custom URL for the serverTokenEndpoint.

(Coffeescript)

devise = DeviseAuthenticator.extend

  serverTokenEndpoint: ENV.apiBaseURL + 'session'
  tokenAttributeName: 'authentication_token'
  resourceName: 'session'

export default devise

Authenticating and Invalidating are ok. But trying to navigate to certain pages I get requests for - https://apiBaseURL/users/sign_in. Which the endpoint doesn't exist.

Why is the configured URL not being used?

Or are there any other places this URL is set? Or used? It's currently causing the page to break and the user cannot continue.