We tried to get this working and ended up giving up after probably blowing a collective 15 hours on it. It's a limitation with the router, it doesn't have great implementation for DHCP options and the 'next server' option is always passed to the clients as the UniFi's address, which breaks PXE booting in this case. It's a problem with most cheap stuff we tried - Ubiquiti, Linksys, Netgear, TP-Link - only our Meraki devices would allow the PXE booting to work properly. Since we have multiple setups for each of us working from home, we ended up just sidestepping the issue in multiple ways, depending on what worked best for each of us. After retiring my Meraki and going with a UniFi device at my home office, I used a separate physical subnet for imaging with my old CloneDeploy system being the actual DHCP server for that network and turned that off on the router. Easy enough for that scenario since it was a separate physical machine, but I couldn't access the UI directly which was annoying, I'd have to remote into the machine with our MDM agent to do that. After switching to toems I now run the server as a VM, and I just use a USB bootable rather than continue to mess around with the separate network.