This seems like network issues between your host and your server. Try looking at some articles for SonicWalls, also, try getting a Wireshark pcap of your network.
My biggest pain point was letting my Check Point firewall handle DHCP. All options were set properly, however the TFTP file name was never passed to the host, so it got an IP, but didn’t know what to do next. I solved this by creating a separate subnet and then letting FOG handle DHCP on that network.
EDIT: Not saying anyone here would willingly gid through your pcap. Take a look at this first video I found on this, could be of some help.