You might try it yourself. I had a similar response from LifePixel when they converted an A7r. On further testing, I found the hotspot they spoke of was at f22!! Way beyond the beginning of diffraction.
I tested the lens myself, and found no hotspots from f2.8 thru f11, which is about all I would use anyway.
On another side, I had a hotspot show up in an IR photo that I put to advantage, won a prize or two with the photo- people think it is the sun. That was in a Canon 50d IR camera.