Melon blocks don’t grow from stems

My melons don’t grow in my worlds even though all my pumpkins do. I’ve waited ages and NO melons appear. I’ve left a block of space, the melon stems are the highest stage, the area is lit up, no mobs are trampling. I didn’t attach an image as it would be a melon stem fully grown next to an empty grass block or dirt block. Cheats were on in survival