A center-lift distortion mode is the most common distortion mode for overall bending. Probably 80% of the slab-on-ground foundations in the Greater Houston Area are in a center-lift mode. This distortion mode is created by the interaction between the foundation and the swelling of the soil underneath the slab.
The reason the supporting soil swells is that the slab itself traps moisture underneath the slab. Typically the soil under the central area of the slab swells the most because the middle area moisture is effectively trapped. Moisture nearer to the slab footprint can escape through evaporation.
You can usually determine what the distortion mode: if there are cracks in the brick veneer and the cracks are wider at the top than at the bottom. the distortion mode is almost certainly center-lift.