Problem solved!

The builder and the developer came and looked at the tile. The culprit, which I already knew, is the clay soil that shrinks and expands depending on the moisture. Fortunately, there is a solution. The broken tiles will be removed and a moveable membrane placed over the crack underneath. The tiles will be replaced and there will be some flexible grout used to allow for some movement. The grout gets hard just like the other, but it still allows for some movement. I learn something new about construction all the time and it's fun. I like learning new stuff. The only problem is that by the next day, I forget it!!! Oh, the perils of aging!!!