We might need to deleted endpoints associated to a particular Username.
If a device authenticates against Clearpass and when a username is updated to that MAC address as attribute during MAC Caching, then we might need to manually deleted if a Unique-Device-Count limit is exceeded.
Navigate to Configuration » Identity » Endpoints. In the Filter select Attribute Username contains <username>. This will display the list of MAC address associated with the username Attribute. We can select and delete the Endpoints.