Looking at your pcap file I would say you have 2 dhcp servers on your network (not a good option).
One is 192.168.5.1 and one is 192.168.5.200.
192.168.5.1 appears to be a router that is passing out an IP address but no pxe boot information. 192.168.5.1 is passing out a client address of 192.168.5.80 to the client.
192.168.5.200 appears to be (maybe) a fog server running either dnsmasq or isc-dhcp server (probably). 192.168.5.200 is passing out a client address of 192.168.5.10 to the client. 192.168.5.200 is sending out a boot file of undionly.kkpxe with a next server of 192.168.5.200.
This seems to be confusing the clients because one time they accept the IP address of the router and sometimes they accept the ip address from fog (which is not providing enough information, but does provide pxe booting information).
Course of action:
Disable the isc dhcp server on the FOG server. Install DNSMASQ to provide the pxe boot information without providing a ip address to the client.