My alpha Hen is a hatchery Barred rock from last spring. She laid from August through March hardly missing a day even in the dark of winter. Then her shells got thin and her productions slowed for a month or two and now she hasn’t laid an egg since May.
Same as you she isn’t sick, doesn’t appear egg bound, isn’t broody and continues to dominate the flock - I think probably just premature ovarian failure? We got another round of chicks this spring so if she still isn’t laying by the time they start, as much as we love her, she’s going to the big coop in the sky to make room.
Not sure if this helps, but you aren’t alone.