Heads Up :
The post you are writing will appear in a public forum. Please ensure all content is appropriate for public consumption. Review the employee guidelines for the community here.
Management API only searches the database for the latest session that contains the specified NAS IP address.
https://<ISEhost>/admin/API/mnt/Session/IPAddress/<nasipaddress>
How about Endpoint(s) that failed authentication or are no more in active ...