I'm suspecting the point in pore space is sometimes too close to the sphere surface to where it confuses openfoam. I've gotten a few packs where I feed it into snappyHexMesh and it either returns me one cell or gives me the inside of the sphere. When I find a point by hand with plenty of distance and use that, it's fine, so I'm thinking that's all it is. I don't know if it's possible to add a little buffer space on the spheres in the algorithm.