Tomato Plants Not Producing Fruit

I have 2 tomato plants growing in my garden, next to each other. One is a Better Boy red tomato plant, and the other is a yellow tomato plant. They are both big and healthy, no signs of any damage or sick leaves. The red tomato plant has at least 20 tomatoes right now, and the yellow tomato plant has not produced any tomatoes at all. Just wondering what could be wrong? the plant appears completely healthy otherwise. It did produce a few flowers, not many, but they died off fairly quickly.

Hardiness Zone: 6a

By gina from Cincinnati, OH