@george1421 Yeah, maybe that was it - just a cold boot after the BIOS update to 'bed things in". Like I said, I was stunned to see the NUC suddenly behaving, so I went back in to BIOS and undid my changes to confirm if that was the cause - still boots w/o issue.
I recall there being a Wiki page somewhere listing hardware that is known-to-work with FOG. Would be good to update that with this information. Not sure if this account has permissions to update…otherwise I’ll create a new one.