Cisco WLAN controller model 4402-25 software version 184.108.40.206 has been configured with CDP enabled yet fails to display the CDP neighbor information of the Access Points that are joined to it. I have looked at each AP and CDP is enabled on each of them as well. I have also looked at the switch configuration that the APs are connected to and it is enabeled on them as well. I do see the CDP information in the switch just not in the controller.
I ran into this same issue with a select few access points, which I found out if the interface the access point is connected to is setup as a trunk port you wont be able to see the CDP neighbors on the controller. I changed the interface to a switchport then I could see the CDP neighbors on the controllers. Kind of weird.