A high assurance session is a type of session security level that requires users to verify their identity using a second factor of authentication, such as Salesforce Authenticator, a verification code, or a security key.
Administrators can configure certain actions or permissions to require a high assurance session, such as exporting reports, viewing encrypted data, or accessing connected apps.
If users are able to run reports but are taken to a login screen and prompted for additional verification when they try to export a report, it could be because exporting is configured to require a high assurance session.
This means that users need to use a second factor of authentication to export reports, even if they have already logged in with their username and password. References: https://help.salesforce.com/s/articleView?id=sf.
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