A global company's Salesforce Identity Architect is reviewing its Salesforce production org login history and...

A SAML SSO ‘Replay Detected and Assertion Invalid’ error occurs when Salesforce detects that the same assertion has been used more than oncewithin the validity period. This can happen if the assertion ID is reused by the IdP or if the assertion is resent by the user. Another possible cause is that the time settings of the IdP and Salesforce are not synchronized, which can result in an assertion being valid for a shorter or longer period than expected. References: SAML Single Sign-On Settings, Troubleshoot SAML Single Sign-On