DIAGNOSIS The freezing cycle is being interrupted too early, so the ice doesn't have time to form fully in the tray. This is almost always a water supply issue.
FIX First, check that the water reservoir is filled to the MAX line, not just a little water at the bottom. Second, press the Cube Select button to ensure you haven't accidentally chosen the "Small Cube" setting—the indicator light should be on for the size you want. Third, clean the water inlet filter (the small screen inside the reservoir where the pump tube connects) with a soft brush under running water.
IF THAT DIDN'T WORK The ambient temperature might be too high. The unit needs a room under 90°F (32°C) to form solid cubes. Move it to a cooler location away from ovens or direct sun.
HEADS UP Using unfiltered hard water can cause mineral scale on the evaporator plate, which also leads to poor ice formation. You need to descale regularly if you have hard water.