We had a manitowoc one time do just about the same thing, and we couldn't figure out why it wasn't harvesting all of the ice- everything looked fine one it, but when it went to harvest it only harvested about half the ice on the grid. after checking it and rechecking it several times, we found out that there were little burrs on the grid where someone had chipped away at the ice with something sharp- causing some of the ice to catch on the burrs and not drop.