There are other methods available as well (static, DNS, DHCP option 43) for the WLC discovery purpose. To verify there is no configuration issues at WLC end, you can simply configure the WLC details on AP statically & check wether AP get register to WLC. To do this you can enter following CLI commands on AP console priviledge mode.
debug capwap console cli
capwap ap ip address 10.38.11.x 255.255.255.x
capwap ap ip default-gateway 10.38.11.y
capwap ap controller ip address
In this way your AP should get registered to WLC (if no config issue at WLC end). Refer this for more detail
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
This is the start of a display filter cross reference between Wireshark
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