To piggy back off this, talked to HP about this earlier today as well. Pre-release BIOS are available but they need to have it approved/signed off before providing it for testing purposes. I was told mid-April is their tentative release date for this.
Anything with a kaby lake processor is having the UEFI PXE boot issues according to them or have had reports. They pointed to the G4 model laptops and the G3+ model desktop machines.