Welcome to the garden.org website. We are seeing a lot of St. Augustine dying off. Rest assured, quite a few yards are experiencing the same problem.
We're in Westlake off 360, and the flatbed trucks, carrying fresh St. Augustine pallets, were a daily occurrence for a while. I have noticed about a 6" half moon ring out from an oak tree in our front yard.
Have you called the Travis County Master Gardeners' helpline? They are very helpful. You can request information mailed to you (for free).