First of all, your batter might be too thin. The batter should be slightly thicker than regular pancake batter, so add more flour if yours is watery!  Or, you might have opened your waffle maker too soon. As the middle of an undercooked waffle is still liquidy and soft, it will easily split in half. Lastly, it might be time to clean your waffle plates thoroughly. As oil and small flicks of batter accumulate on the plates, they will turn sticky.