I installed the hardwood floor myself with the help of someone who has done this before. I agree that it is too soon to be seeing this kind of problem. The flooring is stripped planks with several layers. I forget the manufacturer, but I could look in the attic at the box (spares in case something like this would happen). The flooring is glued directly to the slab foundation. The floor is coming loose from the subfloor and causing a spongy feel as you walk across it. If you hop on the spot, the floor makes a popping noise as it seems that the floor is tacking to the glue and then releasing. Also there are two places where the planks are separating from one another. That starting about a month after installation and are at doorways.
I honestly feel that the spongy area is caused from water that was not cleaned immediately, but am not sure.
Thanks,
Matthew