This IMO is a production fault and lack of quality assurance on the manufactures part, unfortunately they will not accept liability once the tiles are fixed. (States it on every box) That's ok play by there rules next time and fault the tiles before you fix them then watch the tile shop run for cover, let them earn there coin, I get sick to death of seeing this problem week in week out and the only way to get around it is to get the tile shop to keep sending out tiles UNTIL THEY GET IT RIGHT!!!!
I recently done 200m2 of 600x300 porcelain and before I even started I faulted 125m2 with the same issues needless to say the tile shop was not happy with me, but as I kept saying "Stop selling the public S*** that you buy for $5 bucks a meter and then charge the client $45m2 If that ain't enough FAT on your C*** product for me to whinged a bit about a diserning client that commands perfection You'll keep replacing them until I say STOP!!"