sidero: iPXE boot getting stuck on `initialising devices`

Got this same exact setup on both a HP Proliant DL380 and Dell R720.

>>Start PXE over IPv4.
  Station IP address is 10.0.0.X

  Server IP address is 10.0.0.Y
  NBP filename is ipxe.efi
  NBP filesize is 990688 Bytes
Downloading NBP file...

  Succeed to download NBP file.
iPXE initialising devices...

Left it for an hour and no change.