I have a number of WLC controllers and I have something a little odd on one them. When I look in the trap logs on this one particular controller I do not see any Authenticated: messages. I see DeAuthenticated: but not Authenticated:. There are clients associated with the APs on that controller and when you walk in that area with a wireless device it seems to work. I thought it might have something to do with the logging level but those settings look the same as the rest of them. I don't think I am having an operational issue but it just kind of odd on the logging of messages.
Check the trap log controls under MANAGEMENT>SNMP>Trap Controls. Under the client options, is 'Authentication' enabled? usually this is off by default b/c most folks are interested in the failed ones and not the successful ones. Plus, successful ones would fill up the logs quite quickly.