Here is the image with the larger patches and the orange flags mentioned. Thanks!

Sorry to disagree with you weed. That is fungal disease. How long did your grass sit on the pallet before you put it down. St Aug is very prone to disease when it does not get good air circulation. Here is a picture of iron chlorosis in otherwise healthy St Aug... Only the grass in the very center of the photo is affected and only barely affected. I happened to catch it right before the entire lawn turned yellow. I have a much better picture of St Aug chlorosis but on a different computer. Your instinct to spray with a fungicide was correct. I would not have used a spray because I have excellent experience using ordinary corn meal on St Augustine. If the spray does not work, you can still use corn meal but you will have to use a little compost first. Corn meal is a biological solution and your spray has upset the natural biology of the soil. Compost will restore that biology and then you can use corn meal. Yes, this is the corn meal you eat. As a comment on your previous die-offs: the first one was not due to a major freeze. I don't know what it was, but if St Aug survives almost every winter in Dallas, it is much more likely to survive absolutely EVERY winter in Florida. Second one was chinch bugs...or was it lack of water and mowing too low? Established St Aug must be watered at least monthly to remain alive. It needs to be watered weekly during the heat of summer to thrive. If you have sandy soil yours might need it more frequently. And most St Aug should be mowed at your mower's highest setting. Mow too low and you need to use more water...and you get weeds.

If you can, go to Lowe's and see if they have greensand and lava sand. At least mine does up here and I use them on my st augustine lawn that is growing right on caliche soil. Mix both together and spread 40lbs per 1000 sqft. Lowe's has the best price so hopefully yours will have them. Get compost from Garden-Ville (At least i think) for early early start at the rate of 1 cubic yard per 1000 sqft. Use wheel barrow to dump them in various spots and use leaf blower to blow them into the ground till they disappear.It should be one time application forever. Go to animal feed store and get a 50lbs bag of soybean meal (don't tell what its for) as an organic fertilizer and spread 15-20lbs per 1000 sqft with rotary spreader. Do this 3 month. Don't use synthetic chemicals of any kind including fertilizer, herbicide and so on. Mow high at 4 inches. Water very deeply (1-2 inches) only if it is absolutely needed like when 50% of the lawn is wilted. You should have really nice yard by May/June.

How was the soil prepared for the sod? How would you characterize the soil? Is it hard all the time even when wet? Sandy? Does water soak in quickly or stand on top for awhile? That looks like a fungal disease to me. Give the corn meal 3 weeks to show improvement. You have to stop the frequent watering and start with deep watering, but if your soil will not absorb deep watering, then start with an application of shampoo to allow better penetration. Spray any clear shampoo (I like generic baby shampoo) at a rate of 3 ounces per 1,000 square feet. Follow that with 1/2 to 1 inch of water. If you get runoff or standing water before you get at least 1/2 inch, then stop and wait 15 minutes for the water to soak in. Then resume/repeat until you get the 1/2 inch. You can measure 1/2 inch by placing cat food or tuna cans around the yard. Time how long it takes to fill the cans half way. Or for a full inch, time how long it takes to fill the cans. 1 inch is what you should be watering every time you water. With temps in the 110s, that should be once every 5 days. I know this works because we've been promoting it for 10 years on this forum. Also a friend of mine in Gilbert, AZ is doing it with his St Augustine.