Azure Portal asks for a second 6-digit MFA code after Authenticator approval

I can sign in normally to my personal Microsoft account and manage my security and authentication settings.

When I try to sign in to the Azure Portal, I first receive a number-matching MFA request in Microsoft Authenticator. I approve this successfully.

Immediately afterwards, Azure asks me for a 6-digit verification code.

At this point I receive no new notification in Microsoft Authenticator, and the Authenticator entry for my personal Microsoft account only shows an 8-digit one time codes.

I have tried removing and re-adding Microsoft Authenticator to my personal Microsoft account, and that works correctly, but the Azure Portal problem remains.

How can Microsoft reset or remove the Azure-specific MFA registration so I can regain access to the Azure Portal and cancel/delete my Azure subscriptions?