Watering would be one possibility--it looks like it's very close to the house, which depending on how your house is built and what direction the rain comes from, it could be underneath an overhang and not get nearly as much water during rainstorms as plants that are a little farther out from the bed. I'd also doublecheck and make sure the mulch isn't piled right up to the trunk, it needs a few inches between the trunk and the mulch to be healthy.
That sounds like winterburn, but do you even get winterburn in NC? If you do, just water them with cold water once or twice in Jan-Feb. Ours do the same. New leaves will come in afterward so be patient.
When my boxwoods looked like that they had a funfus. Spray with fungicide. Rake all the fallen leaves away from the bush daily. Shake the bush before racking to get as many leaves away as possible. I lost 4 bushes that I did not catch in time. Good luck
Either nutrient deficiency, lack of water or fungus, box is prone to fungus and you need to prune the bush, gather all the pruning and get rid, also as everyone else has said, very close to the wall can mean not enough water, also is there a lot of debris from the house building under the soil, box also needs a feed every year to help it stay strong and healthy, the new growth on box is a paler colour to the mature leaves, but it turns darker green as it matures, so you really need to check out all the suggestions you have been offered here to make sure you treat it the proper way. good luck. WeeNel.
I was pruning my boxwood this morning when I found a problem so have been tooling around of different sites searching major boxwood diseases. There is a serious root rot problem that sounds similar to what you describe.