That is not really a good mix of turf species. I suspect the one dying is the fescue which is a cool season grass needing water to survive the heat. Bermuda is tougher and can brown back and then return from the ground with the return of rains. But bermuda can't take shade, which fescue can take quite well. I suspect you go ahead and mow at about 2.5 to 3 inches and continue to do so weekly to maintain a better, denser lawn.
Let me also refer you to the following web publications that are very helpful in all aspects of maintaining a good lawn in Alabama:
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