All looked normal from the attic side, just an insulated duct box installed like normal with blown in insulation around it. If the stairs were turned a different way you might notice the lack of a register on the ceiling as you were coming down the stairs, maybe, on a good day.
Missing stuff is harder to lock in on than broken stuff.
It was a real Brain twister for me Bruce, thanks for sharing. 
No joke but I can in late
I was going to say a register or exchanger.It only makes sense.I had hot water (closed system) for instant hot water but it was not likely saw no bulk heads if it was an after market item…
IR is a great tool. However, from winter to summer, wouldn’t this senerio change?
Not really. In the winter with the heat on in the house and the attic colder, the area would be basically blue instead of orange. If the attic and house were about the same temperature the IR image would not have shown as much detail but rarely are the two areas that close in temperature for long enough to equal out.
When it is cool overnight, lots of house components hold that cooler temperature for a long period especially if they are not affected by sunlight.