Q: I can't log in to the AMP. I just get returned to the login page. Why is that?
A: If you don't see a reason for deauth on the login page, it means that AMP isn't receiving a session cookie from your browser. You should check your browser's cookie settings.
If you do see a deauth reason, then it's probably correct.
Here are the 5 cases that force a user back to the login page, and the messages that are displayed in those cases:
bad_credentials => 'Login failed. Please re-enter Username & Password.',
logged_out => 'User logged out.',
no_cookie => '',
bad_cookie => 'Login session timed out.',
role_disabled => 'Your role is disabled.',