Boxwoods in Greater Cincinnati are suffering from two problems this spring:  winter damage that occurred when temperatures took a nose dive during the week of Christmas, and high populations of boxwood leafminer.  There are a few diseases that can affect boxwoods but their symptoms typically appear a bit later in the season.

While some boxwoods in our area are suffering from both winter damage and leafminer injury, your pictures look like the problem is boxwood leafminer which produces random leaf brown among leaves that look OK.  Winter injury causes all the leaves on entire stems to turn brown with the pattern usually being from the top down and the outside in.

Here is a posting on boxwood leafminer:  https://bygl.osu.edu/node/2102