Q.Rose of Sharon
Every year a section of my Rose of Sharon dies off but always have new branches coming up. What causes the die off each year?

I'm not sure that it is "winter die off". We had a very mild winter last year. It is rotted at the base and I can just pull it out. However the rest of the shrub is just beautiful. I have two neighbors that have the same problem. [Neighbors are 1/2 mile or more away.] There are ants in the ground around there also. Anymore thoughts?

It is my guess that your plant is experiencing a little bit of winter die back each year. Here is an article with tips on how to protect your plant during winter: https://www.gardeningknowhow.com/ornamental/shrubs/rose-of-sharon/rose-of-sharon-winter-care.htm