You have a freezer with automatic defrost. It constantly defrosts and freezes, and the ice essentially evaporates.
We don't use a lot of ice, and if I don't look at it for weeks, when I do go to get some ice, there is little or nothing. But the evaporation is fairly even. If your other cubes aren't evaporating, only one spot is, I would suspect that you have a water line that feeds an icemaker. We do not have that, we fill the trays at the tap. It's possible that one slot is not getting any water for some reason.