There are several things that cause an icemaker to make hollow cubes. I am sending you an answer from our database that has good suggestions in it. Please disregard the items that don't pertain to you. Some other thing to check, is the refrigerator level? Turn the icemaker off for 2 hours and when you turn it on it should go through a harvest cycle. Watch it as it is filling and time the fill portion of the cycle, it should fill for 6-8 seconds. Check the mold and see if the sections are all full. If the mold closest to the front of the icemaker is under filling, it will cause the icemaker to cycle before the ice is frozen solid. There is a screw on the front of the icemaker for adjusting the fill portion of the icemaker.
There is also the possibility of the icemaker having a bad thermostat, this could cause hollow cubes. The thermostat should be repaired by a technician who will probably replace the icemaker if that is the problem.