Cisco 1141 APs is displaying "not joined" on the Cisco 5508 WLC

[samsaysgo2002]

The WLC version is 7.6.100.0 with 75 AP licenses. I have 64 APs. I have 3 APs not joined now. I can ping all of the IP addreses of the APs from the controller. The controller has the correct time, date and time zone.

There is other APs working correctly on the switch. The ports are configured for trunking like the others.

AIR-LAP1141N-A-K9

(Cisco Controller) >*spamApTask2: Aug 17 14:11:21.287: 00:fe:c8:8f:be:40 Deleting AP 192.168.X.10 which has not been plumbed

*spamApTask2: Aug 17 14:11:21.292: 00:fe:c8:8f:be:40 DTLS connection was closed

*spamApTask2: Aug 17 14:11:21.292: 00:fe:c8:8f:be:40 Discarding non-ClientHello                             Handshake OR DTLS encrypted packet from  192.168.X.10:48640)since DTLS session                                   is not established

*spamApTask2: Aug 17 14:11:21.504: 00:fe:c8:8f:be:40 Discarding non-ClientHello                                       Handshake OR DTLS encrypted packet from  192.168.X.10:48640)since DTLS session                                    is not established

[Leo Laohoo]

Can we see the serial number of the AP?  
This could be FN - 63942 - Wireless Lightweight Access Points and WLAN Controllers Fail to Create CAPWAP/LWAPP Connections Due to Certificate Expiration.