When are you watering it? What may be happening here is several things.

1. You may be watering it too often. That makes for poor rooting as the grass does not feel the need to seek the water further down. Watering 2 to 3 times a week is plenty even in the hottest days of summer.

2. Get a timer. Best to water just as the sun comes up for a good 40 minutes depending on your PSI. Get several empty cat food or tuna cans and place them in multiple areas on your lawn. When they are about to overflow stop watering. Note the time so you know how long to water.

3. Watering in the heat of the day at high sun is the worst as the water evaporates in the heated grass and soil. Worse yet the water droplets can actually boil the grass.

4. Did you fertilize? Depending on the type of fertilizer it too can cause a lawn burn. Always wait til there is a thundershower in the forecast. Fertilize when the lawn first shows signs of growth in the spring. Around the first official day of summer. Late august and when the seasons change in the fall.

5. How short did you mow it? Cutting the grass to a higher length in the hotter months ~ 3 to 3 1/2" will retain the needed moisture.

If you haven't done so already, you might find it helpful to post this in the Houzz Garden Forum.

I do know that one cause of patchiness with Bermuda grass is fungi growth which can be caused by watering the grass at night which I imagine you might have already read about and are avoiding. We've found the recommendation of watering early in the morning to work best because it neither sits in darkness for hours nor is immediately burned by the mid-day summer sun.