boot command hangs

[NiKiZe]

undionly only contains the undionly drivers which uses the initial PXE rom.
so buiding undionly with DEBUG enabled for some other driver will never output anything since that driver isn't included

when you use ipxe.efi or ipxe.pxe that includes the native driver and you get debug output.

I would expect boot to work fine but weird bugs could happen.
Do you have a clean config? if not could you try building with clean?
Also do try to see if ipxe.pxe works differently from undionly.kpxe