When I changed DNN site domain from subdomain.domain.com to domain.com login module not working properly. All users must enter data twice to log in. In DNN event viewer is message 'properly login... ' after first attempt.
Each subsequent login from this machine requires single data entry (login, pass), even if cache will be deleted.

What is the full message in the event viewer?

I have not had this issue reported before.

Problem solved, and was not affected with AS.
In DNN portal alias was only "MyDomain.com" when I add "www.MyDomain.com" login functionality working correct.