As a general rule tiles larger than 12x12 inches should have mortar applied to the back of the tile as well as the floor to help ensure adequate coverage.
Tile floor crackles.
I also think the double wax ring on the toilet has failed as evidenced by the blistering paint in the ceiling board and recessed light below.
Finally tile floors installed over a concrete subfloor are the most susceptible to cracking because the concrete itself is prone to cracking the geeksonhome article states.
For a larger more visible area of cracked tile contact a tile contractor for expert help.
As long as the tile does not break under 250 pounds of pressure the tile is considered to be compliant with these standards.
Most tiles meet the 250 pound minimum.
However cracks wider than 1 8 inch will eventually transfer to the tile it.
Sometimes hairline cracks in tile floors are one of the first tell tale indications that soil or moisture is affecting a foundation.
Ceramic floor tiles especially larger tiles need an even distribution of mortar underneath them.
Most tiles comply with astm c648 breaking strength standards.
In many cases cracked tile floors are signs of foundation issues it s possible that soil movement or water has caused your foundation to shift move or even be pushed in an upward direction.
Generally hairline cracks in the concrete will not present an issue to the tile floor above.
In this test floor tiles are run through a machine that exerts loads on an unsupported 1 inch square area.