We're also facing this issue. We have two anchor WLCs and 4 foreign WLCs in a guest WLAN design (incl. ISE). Only one of the four controller showed this behavior. The interesting thing is that all four foreign WLC are in the same network (VLANs, etc). So there should not be any difference in DHCP round-trip time. We will restart the affected WLC and check if the behavior stays the same.
