Explanation

Microsoft enforces a strong default two-gate password reset policy for any Azure administrator role. This policy may be different from the one you have defined for your users and cannot be changed. You should always test password reset functionality as a user without any Azure administrator roles assigned.
With a two-gate policy, administrators don't have the ability to use security questions.
The two-gate policy requires two pieces of authentication data, such as an email address, authenticator app, or a phone number.
User3 is not assigned to an Administrative role so the configured method of Security questions only applies to User3.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/authentication/concept-sspr-policy#administrator-passwo