Moleanos Bush hammered stone can break down for many reasons.
The process of bush hammering effectively opens the pores of the stone.
Sealing is essential to maintain the protective barrier against water & frost penetration.
If the stone is not maintained & sealed correctly, the elements and general traffic can cause the limestone to crumble.
I can see from your order that this has been installed since 2014, and you did not purchase any sealants from us at the time.
If your installer did not seal the tiles, and you have not kept up the maintenance, you will not be able to restore the damage, and the tiles will need to be replaced.