Q.What Causes Dead Branches On Holly Bush?
My established holly bushes are on the east side of the house and every year there are a few dead branches; completely dark brown/black. It doesn’t look like the pictures of winter burn I’ve seen.

Certified GKH Gardening Expert
Unfortunately, your photos did not come through. I am unable to see the damage. You did mention that it is on the east side of your house, which would give less sun if you have the shade from the house on it. This might leave the soil a little more moist. This can cause root rot. Some species of root rot will have a smell to them. You might try and confirm that there is a smell, though this isn't a good way to test for rot. Many do not smell strongly.
This article will offer information on the treatment, and prevention, as well as testing information:
https://www.gardeningknowhow.com/plant-problems/disease/root-rot-in-garden-plants.htm