If your cracking is in straight lines across several adjoining tiles refer to another Tile Doctor segment on cracks.
The tiler has not achieved full coverage of adhesive under the tile and there will be a 'void' under the tile. When pressure is applied to that tile, it will crack. This can be a chair leg, table leg or even someone walking over that tile with stiletto heels. The pressure on that section of tile, if it is not supported will cause it to crack or break.
It is easy to find if this will happen to any more tiles in the installation, or if it is an isolated one or two. Tap the tiles with a hammer handle or screwdriver handle. Where there is a hollow sound, there is a void below the tile and that tile is a contender for a future crack.
The tiles were not laid correctly and rectification is needed.
The damaged tile or tiles should be removed and replaced by the tiler or builder who is responsible. While they are on the job, a check should be done for any other tiles that are also drummy.