There is no limit to the number of shadow Pieces spawn by mining sculptures

I think this is intended.

And even if it weren't, I'm glad game gives opportunity to gain multiple shadow atriums per new moon through more difficult/risky fight, for example, via fighting knight + bishop + 2 rooks. One also can chain shadow clockworks for multiple atriums as well, and even through it won't match time and resource efficiency of many people's favourite cheese, I think more ways to do his fight benefit game in general.

 Dear person, stop trying to ruin my happiness, let me live with my cheese