Overall, I think the plant looks healthy.
The stems that support the dead and dying foliage were probably damaged or injured somehow. They can't carry water and nutrients to the leaves growing above, so those leaves die.
You could reach into the plant and snip off those damaged stems removing the dead foliage that way. Or you could just rub the dead leaves off once they become brittle enough. Or you could leave it alone. The leaves will drop off by themselves eventually.
Something damaged those stems. The trick is figuring out what it was and not allowing it to happen again, in other parts of the crown. The little "holes" you leave by trimming will heal over.
