@brad-chamberlain If you edit the dhcp config file make sure you restart the isc-dhcp service.
The next step is to see what the dhcp server is telling the client. The easiest way is to use tcpdump to capture the dhcp process.
https://forums.fogproject.org/topic/9673/when-dhcp-pxe-booting-process-goes-bad-and-you-have-no-clue
You can use tcpdump on the fog server or install wireshark on the fog server if you have the Xwindows ui installed. For wireshark use the capture filter of port 67 or port 68 or port 69 or port 4011 Start tcpdump/wireshark and then pxe boot the target computer to the error. Then stop the capture.
Review the pcap with wireshark. You should see the DORA process (Discover, Offer, Request, Ack/Nak). The target computer will send out a DISCOVER packet, look at packet at dhcp option 93 this will be the target computer saying what type it is uefi or bios. Then look at the OFFER packet from the dhcp server. In there the header should be set with {next-server} and {boot-file} matching dhcp options 66 (fog server IP) and option 67 boot file name. The answer should be in the dhcp process. If you can’t spot it upload the pcap to a file sharing site and either DM me the link or post it in the thread and I’ll take a look at it.
The dhcp settings you copied from the coexistence page should be accurate.