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Yeap, you describe it exactly and unfortunately we still don't have an answer. It's not caused by an out of sync MFA prompt as I have personally looked at a number of cases with the user as stepped through it. Out of 140 staff the problem seems to occur once every 2-3 weeks on average. The modern auth prompt happily accepts the password and moves on to the MFA stage so the password has been accepted as correct, the MFA auth (ie SMS) is then generated and the user types in the code to the prompt, clicks OK, it thinks for a second or two and then prompts the user for the password again. The problem appears to randomly affect users (I've had it affect myself once too), and the only solution appears to one of (or a combination of) the options in the OP. In the instances that this occurs the effected user is not new to MFA but has been running it for at least months.
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and so we repeat the same process again, and again. Then a couple of seconds later the modern authentication screen appears again asking for your password. You approve the sign in on your phone then the authentication window on the computer closes. Please respond to continue" (I am using the Authentication App but the same problem occurs if you are using SMS). You enter the correct password then click 'Sign in', You are then displayed with 'We've sent a notification to your mobile device.
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Has anyone else experienced Outlook 2016 stuck in an authentication loop when you have multi-factor authentication (MFA) enabled on Office365? The sequence is that Outlook displays the modern authentication screen for you to enter your password.
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