Because so many of them are warping the same way it looks like this is an issue of expansion/contraction. The sun shining on the floor heats up the tiles faster than the concrete below them. Maybe the person below you is running their air conditioner while you are not. I always wondered why the grout lines were so wide: Grout joints also allow for contraction and expansion of the tiles; outside installations exposed to hot summers and cold winters will fail if they are not set correctly and properly grouted. Inside, tiles can buckle and come loose if not properly set with adequate grout and the occasional expansion joint. https://www.tilelines.com/grout/ I am a bit picky when it came to grout lines in my tile floors. I always required that the grout be steel troweled with a spoon after the grout began to set up. This hardens and seals the surface. Tile setters vehemently resisted doing this when I asked and then demanded. I always paid a helper by the hour to do this as the tile setters do not factor in the time when they quote the job. They positively reflected on the results after they finished. It is the same as finishing concrete with a steel trowel after it has been floated and the bleedwater sheen has disappeared. https://www.concreteconstruction.net/how-to/tools-of-the-trade-and-how-to-use-them_o Typically grout is washed with a wet sponge. This washes away the fines and leaves a rough surface that entraps dirt and stains.