This is a sidewalk grip where it ramps up from the street. I noticed that all of them have the same melt pattern. Low traffic area when no one was out.
Here is what the underside of that particular plate looks like. The metal heats up faster than the concrete as the temperature rises, so the parts with thicker metal melt faster.
The material underneath the top layer will impact how the material temp changes.
It looks like it has some underlying material that is in the square and X shapes that is either retaining heat at a different rate that the surface material or possibly absorbing heat from the warmer ground mass that isn't as cold as the surface and it is enough of a difference for the snow to melt faster there than the surrounding area.
In addition to the possibility of reinforcement bars it could also have to do with the thickness of the tactile pad or it could have recessed spots underneath (to save on material if it was injection molded) that could create an insulating air gap.