First thing to check with all vWLC cases
Connectivity problems of any sort: radius timeouts, client ip connectivity, ap's unstable
check vWLC's message log. if you see this:
#LOG-3-Q_IND: dhcp_proxy.c:3754 Received a DHCP packet sent by the controller itself possible network loop![...It occurred 5 times.!]
With a very high degree of certainty, the issue documented in this bug is the cause:
CSCuj14843 vWLC: prevent service/data port confusion
To fix:
via the vWLC's vm, create a new vswitch that is not mapped to a physical nic.
map the service port to it
save the vWLC's config and power cycle the vm