You have a healthy plant. The older leaves will fall off. But the leafless bulb contributes to the overall plant.

There are two types of leaves on sympodial orchids. One type grows from the top of pseudobulb and another type grows on the sides. These on the sides will fall of, it is normal. Top leaves will fall of from old p-bulbs, this is normal too. Old p-bulbs will become yellow and dry out - normal process.