Barberry shrub invasion
Montgomery County Maryland
We cannot make an accurate diagnosis from your photo. This looks like adventitious roots on the stems. It may disrupt the vascular tissue. Reaons for this include possible herbicide damage, a bacterium, fungal issues, etc.
Monitor and prune back dead branches and throw in the trash. Prune back to healthy tissue.
Here is some information. Barberry is an invasive plant and we do not recommend planting them. They spread by seed and vegetative means and displace our native plants. Barberry seed is transported to new locations with the help of birds and small mammals which eat it.
You may want to take the opportunity to plant some native species as a replacement. https://extension.umd.edu/hgic/topics/japanese-barberry