This before pictures shows a settlement crack through 3 tiles as well as where the installer likely sanded down a raised tile edge. Raised tile edges can occur with the best installers. Often the installer will sand down the raised travertine edge because it stands out like a sore thumb.
However the consequence in doing so exposes the small voids, air pockets, within the stone body. This then allows soil to get trapped and difficult to remove without professional cleaning.
The solution, as we did with this floor in Orlando, was to grind floor flat and fill the resin based filler, filling the smallest holes, grout lines and cracks. The customer desired a high polish and we delivered.