Central Dead Zone

There are a number of reasons that a shrub may get such a dead zone. The most common is age. As the plant continues to grow, it shades out the middle and the leaves there die off. This leaves just a zone of leafless branches. The other common reason is pruning at the wrong time of year. Most plants resent being pruned when it is very hot, and it often either kills part of the plant, or greatly reduces its vigor. The third reason this could happen, which is remote in this case, are root fungal infections. There are many different types, but they tend to present as death of a segment or limb, suddenly and without cause. Suggest you take a sample or this photo to a local nursery or the extension service for confirmation of the exact cause.