One of the reasons for this could be that the node from which the Clientless user is logged on to Cyberoam is not defined under Auth Network of Local ACL. Go to Firewall > Local ACLs and add the node from which Clientless is logged on to Cyberoam.

Please note that in Manage Clientless user list; only deactive clientless users will be listed. By default, Clientless user will always be active and will be displayed in the Live User list.