In the last 6 - 8 weeks I’ve seen occasional brown branches in among the green. When I pull them out they appear to have been severed from the main stem. One of the pictures attached shows that some of the leaves are brown, the branch has already separated, and it is on its way to dying. It doesn’t appear that the branch dies and then breaks off. The browning happens randomly and is in all three of our bushes. . Bushes planted in 2001 on the south west side of the house. Get a load of sun in the summer and of course it’s been hot and very dry this year. I am on Kent Island where we have had less rain even than many others.
There is no disease or insect known that would cause this.
The cut stems suggest animal gnawing. While voles are known to gnaw on boxwoods, it is possible that a larger animal may be biting off stems in their search for water because of our record-breaking drought.
You might try putting out a water source for wildlife, at least until we get some rain. A pan of water at ground level should do it.
Here is info on voles: https://extension.umd.edu/hgic/topics/voles