Thanks! I've added your results and johnnie.black's results to the initial report, here, as a comparison of all of the boards. As you can see there, there is not one suspect difference found, so I have failed to find a significant clue, so far. There are still possible differences in how the UEFI is configured in the systems, and perhaps the non-working systems should report anything in their UEFI setup that is not default.
I didn't know that existed! And it actually works (even on the phone)! Awesome, thank you!
This is interesting, and I'd like to know if IPMIView (or any other tool) has a screen buffer for the console, preserved even after the reboot. The problem here is that what we really needed to see was the console messages (or dmesg) up until just before the reboot, on the rebooting systems, but that hasn't been possible. If the second machine can capture the screen and still have it after the reboot, then we can know either the last error, or at least how far it got, and can narrow the suspects down.
I am downloading an eval copy of SuperMicro's SUM now, which should allow me to dump the current BIOS config once I figure it out. Unfortunately I'm now one state over from my server, so getting a direct screen capture isn't possible. If I have a chance and IPMIView seems to work stable, I'll see if I can figure out a way to capture it.
Attached are the current BIOS config, and for completion, the DMI config. SuperMicro was super helpful in giving me an eval key for SUM!
dmi.txt
bios.txt