The changing color and leaf drop could be a sign of too much water at one time.  Heavy rains are causing problems. Too little water can cause the same symptoms but is usually accompanied by leaf scorch on other leaves. Check how wet the soil is under the plant and pull back the mulch if it is soggy. Soil should be damp but not bone dry. Check the soil to a depth of about 2 inches before watering as well as making sure your shrub is getting enough water. It will need extra care during the very hot weather. It also looks like the bunnies are pruning your shrub. It may need to be fenced, especially this winter to prevent them from eating all the branches.