Thanks everyone for the support.
@Daniel-Miller and @Sebastian-Roth I opted for the approach you suggested of making TFTPD ‘correct’ the filenames. The affected PC now goes to the FOG menu. I missed Sebastian’s map file and ended up writing my own which is:
# Workaround for PXE clients that misinterpret the DHCP options # because they expect a null-terminated string # match the extensions followed by any characters and replace it with # just the extensions r \.pxe.* \.pxe r \.ipxe.* \.ipxe r \.kpxe.* \.kpxe r \.kkpxe.* \.kkpxe@george1421 I wouldn’t even have guessed that proxy DHCP was a thing. I’ve decided not to go for it this time but I’ll keep it in mind for future.