Hi,
1. Please check the output for the following command to see if there are available addresses in the DHCP Pool
show ip dhcp statistics
if there are no free addresses, you can probably reduce the least time for the guest users or increase the size of the guest subnet & reconfigure DHCP pool accordingly (make sure if subnet change is done, it should be done across all the l3 interfaces which have IP on the guest subnet).
2. If there are free addresses & client sitll gets an APIPA address, get the following outputs while the client is stuck in getting an IP address:
config# logging level debugging network process dhcpd subcat all
# show station-table | include <mac-address of user>
# show log network all | include <nac-address of client>