@fierke A correction to my last post. The fix is now merged into working-1.6 and rc-1.6.0. Update your checkout and re-run the installer. The installer now writes default.ipxe without those two lines, so you do not need to comment them out again.

You are right that this can happen on other machines too. Any UEFI firmware that never ends its variable list hangs the same way. The update fixes it for all of them.

I would still like the show efi/SecureBoot result and your BIOS version when you have time. That confirms the cause before the iPXE side ships.