What does your builder and painter say?

Says it’s the lighting! Which baffles me how this can ever be acceptable

You should know the process and materials used. It would help us if you listed them. Once you get that info forward it to Tech Support at Hardie for their recommendations. Here's some discussion relating to primer, which could be a contributing factor to the finish you have. painting hardiplank siding - Fine Homebuilding

It seems if the product came primed, washing, sanding and repriming with acrylic primer is an option to help produce a quality finish when you then apply a 100% acrylic topcoat.

This variation isn't lighting.