now that I can login (and changed my password) for the Q&A hub, I tried logging out and got the following error:
I can reproduce this error. Login is working just fine per sso.
EDIT: The password change didn't take. I had to use the initial password again to login. So it seems, my profile changes aren't saved (avatar is also back to default).
If you tried the profile and settings that you see in the header in Q&A, that will go away, so it's good that your changes are not effective there. You will only have your Universal User Profile, the AnswerHub profile will be turned off, now we are only having it for testing purposes.