My point about the insulation relates to whether the insulation covers the blower inlet. If it does, then you are correct - and I asked this,
I misunderstood, as I said. It doesn't cover the hole. Now I suggest you estimate how much heat will reach that point. Start with 50 W. Remember, there is no anomalous heat; the effect you postulate is being caused by the instruments measuring 50 W incorrectly. Take into account the fact that 95% of the heat is removed by the moving air, as you see in Fig. 2. That leaves 2.5 W. Now estimate the solid angle based on the distance from the reactor to the top, and the size of the hole, 5 cm. What fraction of those 2.5 W reaches through that hole? I suggest you calculate this, although you seem strangely allergic to doing a quantitative analysis of your own hypothesis. So let me take a crack at it . . .
The reactor is a 12 cm diameter cylinder, 50 cm long, sitting at the bottom of a 70 cm tall box. The hole is a circle 5 cm in diameter, ~8 cm^2 area. Assume the 50 W is distributed evenly over the entire surface of the cylinder, but none comes out the end. Assume it is directly under the hole. The heat radiates in all directions equally. 5 cm is one-tenth of 50 cm length, so 1/10 of the heat that is not removed by the air radiates from a 5-cm segment. That's 0.25 W.
I am going to treat this 5-cm segment of the cylinder as a sphere, because my geometry is rudimentary. The diameter puts the center of the cylinder it 6 cm above the floor, so you can think of it as a sphere 64 cm in radius by the time it reaches the top of the box. The solid angle is . . . ummm 0.002 sr. See:
https://rechneronline.de/winkel/solid-angle.php
An entire sphere is 4 pi = 12 steradian. The imaginary sphere is 64 cm in radius, 51,472 cm^2 in surface area, or 25,736 cm^2 per hemisphere. 0.002 sr is 0.0003 hemispheres, or 8 cm^2 out of 25,736 cm^2, or 0.03%. To put it simply, we have 8 cm^2 piece of the surface of a sphere with 51,472 cm^2 surface area, which is 0.03%.
In other words, 0.03% of the 2.5 W of heat reaches the hole. Right? That's 0.08 mW.
You want to check my arithmetic? Please do.
Now explain how 0.08 mW can raise the temperature of the air by 10 deg C. That 10 deg C cannot be an error in the two RTDs on the top, because it is confirmed with other temperature sensors.