The stone and grass blocks generate because that's where the structure data mode blocks were that generate the mobs, they seem to replace them selves with the block that was there before the structure generated instead of air like they are supposed to.
Supernova3695Yt
The stone and grass blocks generate because that's where the structure data mode blocks were that generate the mobs, they seem to replace them selves with the block that was there before the structure generated instead of air like they are supposed to.