But it does sorta look like fungus.
Where do you live in Utah?
When did you use fungicide last? What was the temperature?
When were the last two times you fertilized and what did you use?
How do you water (frequency and duration)?
Do you know how long it takes your sprinkler to apply an inch of water? The only way to know is to put out several cat food or tuna cans and measure how long it takes to fill them.
What kind of grass do you have?

Be sure you have no leaks in your sprinkler system and that the sprinklers are throwing the water and not dribbling.

The 90 degree F temp was too high to use any chemicals. That's why the fungicide didn't work. Read the label and you'll find you are very limited as to the times of year they claim it works. In Texas that time of year is about Valentine's Day. The rest of the time it is too rainy or too hot.

Since 2002 I have been very happy using ordinary corn meal to kill disease in my lawn. Cracked corn works fine, too. Corn gluten meal is a similar sounding material but costs a lot more and does not seem to take care of the disease. Ordinary corn meal is what I'm talking about. Apply at 20 pounds per 1,000 square feet and water it down (not in). Just wash it off the grass and you're done. Reapply in 3 weeks and any disease should be gone in a month. The corn is a biological approach that brings in microbes that feed on the disease microbes.

This time if year you should be watering no more than once a month in northern Utah. That should be a deep watering of about an inch. When you get an inch of rain, then you don't need to water.

I hate rain birds. The only advantage they have is being able to throw water upwind. My absolute favorite sprinkler is the oscillator. The new turbo oscillator sprinklers are great. I have five of them at two houses and will be getting a sixth next spring. They apply water very evenly and very slowly to allow it to soak in without runoff. For a rectangular yard like yours, they would be perfect.

Mow at about 3.5 inches when you mow.

If you want to use Scott's chemical fertilizers, follow the directions for timing. I think you went a little heavy in the past 6 weeks. If you want to apply organic fertilizers that frequently, GO FOR IT. You cannot over apply organics, and they just make the soil better and better. Generally lawns need nitrogen once in the spring and twice in the fall. The twice in the fall come once after the summer heat breaks and again right before dormancy. Your timing in the past 6 weeks seems too close together but it might have been exactly right. Just seems close together. One of the lawn gurus on another forum has tried to overdose with organic fertilizer. He's applied up to 50 pound per 1,000 square feet per week for every week of the growing season. The only thing that happened is his KBG lawn remained green deep into December and greened up again in January. From that experiment I say you cannot overdose with organics. Try that with chemicals and you'll sterilize your soil for years.

If you want to take your lawn to the next level (once you have control over it), get a soil test at Logan Labs in Ohio. Their $20 test is much better than most university or county extension service tests costing up to 5x more.

Notice the improved color, density, and growth.