Ok from what i understand, this paper is proposing that a very specific substitution of the Copper atom in the place of the lead atom in the lead apatite structure is responsible for this

This only happens at a very specific atomic site but it alters the structure of the material in a way that creates a "Flat Electronic Band" that is key to Supercon

But since it has to be at that very specific site at a very specific atomic proportion it could explain why people are having trouble replicating this material exactly

https://arxiv.org/abs/2307.16892