Intermittent EFI boot issue?

[Jason Hunt]

Intermittently after building world/kernel and installing kernel, upon
reboot I sometimes get stuck at:

>> FreeBSD EFI boot block
   Loader path: /boot/loader.efi

   Initializing modules: ZFS UFS
   Probing 35 block devices ... done
    ZFS found the following pools: zroot
    UFS found no partitions
Consoles: EFI console

And that's it.

Often times it's fixed by rebooting, but sometimes it takes numerous
attempts.  Patience and cold boot vs warm boot doesn't make a difference
and unfortunately there doesn't seem to be any pattern as to how it fixes
itself.  Eventually the full boot screen appears and I can get in to single
user mode to continue installing world.

I've only been following current for a couple of months, so I can't say if
this is a new problem, but it's happened most (but not every) times I've
rebuilt the system.  Normal day-to-day rebooting doesn't give me any
issues; only when rebuilding.

Do I potentially have a buggy EFI firmware (motherboard is an ASUS P8B75-M
with latest firmware), or could it be a FreeBSD issue?  I'm not even sure
how to try diagnosing this or what information would be helpful?

Any suggestions are appreciated.

- Jason