System-preferred MFA not (quite) working as expected

[TH]

So I've ran into an interesting issue in my tenant today while checking some reports on the usage of various authentication methods.

We enabled system-preferred MFA for all our users a few months back. Of the approx. 4K users that have MS Authenticator installed and configured (where some are capable of passwordless as well), it seems that over 20% of those users still have SMS as the Default sign-in method registered.

Any idea what might be the cause of this? Where/how to investigate this further?

Is there a configuration we missed, or is system-preferred MFA a little buggy still? Thanks for the feedback! 

[#2]

if a user registered both SMS and Microsoft Authenticator push notifications as methods for MFA, system-preferred MFA prompts the user to sign in by using the more secure push notification method.

[#3]

@Chandrasekhar_Arya 

Yes, I'm aware of how it should work, it's just that it doesn't affect all our users as I described above.