When a user chooses to NOT save their password in SfB mobile client, why does DOS show 2 failed login attempts when the user only ever attempted to click on Sign-in once?

The client will sometimes automatically retry invalid credentials.

Also, at least two NTLM authentications happen during sign in, one is to sign in and the other is to obtain a client certificate.

Obtaining a client cert isn't something that happens on every sign in.