Hi there,
It could be any number of things that is causing this issue.
-Web application is holding onto identity (or cookie isn't getting cleared)
-ADFS is sending the same user token for both users (unlikely)
-ADFS is caching user identity
-Proxy between ADFS and web application is caching token
You can use fiddler to watch the token move across the wire, and that should tell you what is happening exactly.
You can try some additional troubleshooting steps grin this article
https://learn.microsoft.com/en-us/troubleshoot/windows-server/identity/troubleshoot-ad-fs-sso-issue
I hope this information helps. If you have any questions please let me know and I will be glad to help you out.
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