Hello Neha,
The problem is that AD FS rolls over its token-signing certificate automatically, but your SaaS applications are still bound to the old one. When that happens, tokens signed with the new certificate are rejected. The quickest way to fix this is to update the relying party trusts with the new certificate. If the SaaS app supports automatic federation metadata refresh, enable it in AD FS by opening the relying party trust properties, going to the Monitoring tab, and checking “Automatically update relying party.” If the app doesn’t support that, you’ll need to manually provide the new federation metadata XML from AD FS at https://<your-adfs-domain>/FederationMetadata/2007-06/FederationMetadata.xml.
For environments where downtime is unacceptable, many admins disable automatic rollover with Set-ADFSProperties -AutoCertificateRollover $false and manage certificate changes manually, so they can coordinate with SaaS vendors before switching. If you’re already broken, export the new token-signing certificate from AD FS and import it into the SaaS application’s trust configuration. Once the SaaS side trusts the new cert, logins will resume. Long term, the best practice is either to configure automatic metadata consumption or to plan certificate updates in advance with vendors.
I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!
HP.