Cisco 5520 Wireless Lan Controller unable to connect access point using wired connection using POE injector using CDP I can see access point but unable to have it show up in access point list. The access point is directly connected to WLC, with no switch or router but both AP and WLC are using ip in same subnet /24.
Also, check compatibility. As you upgrade WLC firmware, older APs will not show up, because their firmware will drop off the compatibility list. This can even happen with APs that are currently connected. Install an upgrade to the WLC, and a bunch of APs disappear.