Hi, 

This looks like some old boxwood mite damage, possibly some signs of Volutella blight, and maybe just general stress if they weren't checked for water periodically (this year and last year during the drought).

You can prune back any leafless or unhealthy-looking stems and wait for regrowth in spring; if the plants are too shaded, that will suppress new growth from the interior/base of the plant, which ordinarily fills in readily when there are gaps in the canopy like this.

If you want to fully rejuvenate the plant and keep regrowth more even, then the whole shrub can be pruned back in spring to let it fill in more symmetrically, although it will take a few years of regrowth to get back to this size since Boxwoods are slow-growing plants. 

You can refer to our Boxwood diagnostic page for information on Volutella, boxwood mites and how to properly prune. 

Let us know if you have further questions. 

Emily