Unreliable PXE-booting of Quanta S910-X31E

In doing 17.04 regression testing of a Quanta STRATOS S910-X31E server, I'm having problems PXE-booting the server for enlistment, commissioning, and deployment. The symptom is that the server (which is configured to boot in EFI mode) successfully downloads GRUB, but GRUB seems to be unable to retrieve its configuration and follow-on files from the MAAS server computer, resulting in a "grub>" prompt on the Quanta server's display. This does not happen on *EVERY* boot, though; on about 1 in 10 attempts, the server *WILL* successfully PXE-boot from the MAAS server, at which point the requested operation (enlistment, commissioning, or deployment [with caveats]) will succeed. Note that on deployment, the system must PXE-boot twice -- once to install the OS and again to reboot into it. This second boot produces the same type of failure as the first one, so the deployment is likely to fail. I have gotten it to deploy by watching the screen and resetting when the "grub>" prompt appears; if I'm lucky, the system will boot with few enough failures to avoid a timeout in MAAS.

I have attempted several workarounds, none of which has helped:

* I've reconfigured the system to boot in BIOS/CSM/legacy
  mode rather than EFI mode. The server seems to be unable
  to PXE-boot at all in this mode, though; it goes straight
  to the firmware setup utility. Perhaps I'm missing a key
  setting, though.
* I've configured the server's second (of two) network
  interface to enabled without PXE-booting. This has no
  effect.
* I've configured the server's second network interface
  to disabled. This does not help; and if done during
  commissioning, results in MAAS thinking the server has
  just one network device.
* I've tried quitting out of GRUB. When multiple network
  devices are enabled, this results in an attempt to PXE-
  boot from the second device, which produces the same
  failure as the first.

Although I discovered the problem with Ubuntu 17.04, I've tested with deployment of other versions (primarily 16.04), and that has not helped.

This server was successfully deployed and certified on November 3, 2016:

https://certification.canonical.com/certificates/1611-10128/

Thus, it appears that this problem is new.

Other servers I've been regression testing have not exhibited this problem, so I don't think it's a MAAS configuration option -- or if it is, it's something that's affecting just this one server (oil-moltres; MAC addresses 2c:60:0c:73:75:8c and 2c:60:0c:73:75:8d; BMC IP address 10.245.32.2). I'm attaching the /var/log/maas directory tree from the MAAS server. (Note that I'm taking that image during an ongoing deployment that has finally begun to work, but there were quite a few failures shortly before that.)

MAAS version information is:

$ dpkg -l '*maas*'|cat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-===============================-==============================-============-==================================================
ii maas 2.1.4+bzr5591-0ubuntu1~16.04.1 all "Metal as a Service" is a physical cloud and IPAM
ii maas-cert-server 0.2.30-0~74~ubuntu16.04.1 all Ubuntu certification support files for MAAS server
ii maas-cli 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS client and command-line interface
un maas-cluster-controller <none> <none> (no description available)
ii maas-common 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS server common files
ii maas-dhcp 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS DHCP server
ii maas-dns 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS DNS server
ii maas-proxy 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS Caching Proxy
ii maas-rack-controller 2.1.4+bzr5591-0ubuntu1~16.04.1 all Rack Controller for MAAS
ii maas-region-api 2.1.4+bzr5591-0ubuntu1~16.04.1 all Region controller API service for MAAS
ii maas-region-controller 2.1.4+bzr5591-0ubuntu1~16.04.1 all Region Controller for MAAS
un maas-region-controller-min <none> <none> (no description available)
un python-django-maas <none> <none> (no description available)
un python-maas-client <none> <none> (no description available)
un python-maas-provisioningserver <none> <none> (no description available)
ii python3-django-maas 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS server Django web framework (Python 3)
ii python3-maas-client 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS python API client (Python 3)
ii python3-maas-provisioningserver 2.1.4+bzr5591-0ubuntu1~16.04.1 all MAAS server provisioning libraries (Python 3)