Why do some of my bell peppers wilt during the growing season?

They are thirsty

https://www.gardeningknowhow.com/edible/vegetables/pepper/pepper-wilt-on-plants.htm

The simple answer is, it’s too hot and the plants need more water at the stem-growing period to have strong stems, but not so much water that the stems can’t absorb nutrients from the soil Or from fertilizer you add. The next reason for wilting pepper plants is bugs. Check under the leaves, on the stems, at the root, at the stem-pepper connection. All kinds of insects can attack your plants, except earthworms. They keep the dirt aerated, which is a good thing. And sometimes, some plants are just healthier than others. Happy gardening! ☺️

If it's too hot or they don't have enough water, peppers will wilt. Pepper plants may also appear wilted if they are not given the proper support for growth