Unexpected SMS Verification Codes and AMC PROD Sign-in Attempts Across Multiple Users in Entra ID

We are seeing a large number of failed sign-in attempts across multiple users in our Microsoft Entra ID tenant involving the Microsoft first-party application AMC PROD (App ID: 81feaced-5ddd-41e7-8bef-3e20a2689bb7).

Observations:

• Multiple users receive unexpected SMS verification codes daily.
• Sign-in logs show Interactive User Sign-ins.
• Client App: Browser
• Authentication Method: SMS Sign-in
• Common Error Codes: 54010, 53003, and 50074
• Failure Reason: "Proofup blocked due to credential used not supported."
• Sign-in attempts originate from multiple countries including Russia, Indonesia, Belarus, Japan, Brazil, and others.
• Password resets do not stop the SMS messages.
• Conditional Access blocks or interrupts many of the attempts.

We understand that AMC PROD (App ID: 81feaced-5ddd-41e7-8bef-3e20a2689bb7) is a legitimate Microsoft-managed application. However, our concern is:

1. Why are users receiving SMS verification codes when they are not attempting to sign in?
2. Why is AMC PROD appearing as an interactive browser sign-in rather than a non-interactive Microsoft service operation?
3. Do these events indicate external actors initiating authentication attempts against user accounts?
4. Has anyone else observed similar AMC PROD sign-in behavior across multiple users?
5. What is the recommended mitigation to stop these recurring SMS verification messages?

Any guidance from the Microsoft Entra product team or administrators who have experienced this behavior would be greatly appreciated.