The separated core on the right hand bullet shows lack of any bond as the smooth lead side indicates where it was incontact with the inside of the jacket.
: Rarely is one box of bullets made on the same machine or even in the same batch, unless from a very low quantity custom shop. Is it possible some of the bullets in those two boxes you've got, were from a batch that escaped being bonded. I don't know their process, so can only suggest possible cause.