Either Scale Insects or Bermuda Mites. FWIW your Bermuda should be fertilized once a month.

This is a st. Augustine lawn. I do have some bermuda and other crap mixed in from when I bought the home last year.

Any ideas? Too high or low ph? Disease? Infestation?

Where do you live? I live on the edge of the Texas desert in the middle of a drought and have only watered once this year. I would suggest you might be watering waaaay too often and that might contribute to a fungal disease. Is that sand in one picture? Living on sand can be a little challenging. When you do water, how long do you water?

Are those spots the same spots where your wife laid piles of leaves or other garden trash for several days before anyone picked them up? Because that is what my yard looks like when my wife does that. If that rings a bell, then it is a fungal disease that will not stop spreading until you do something. Since 2002 (when I went organic) I have had good success stopping it with ordinary corn meal applied at 20 pounds per 1,000 square feet over the entire yard. In fact the entire reason I went organic was due to the success of corn meal in killing this fungus. Nothing I tried had worked before the corn.

Anyway, even if you can't remember anything cutting off the air flow to the lawn in those spots, it still looks like a fungus.

You applied fertilizer about 6 weeks prematurely. The grass coming back from winter would have looked dark green with or without fertilizer.

At this point, in addition to the yellow spots, it looks troubled. It is thin. And are yoou mowing at the mower's highest setting? Without getting the reply to my questions, I'm going to suggest watering less often but more deeply, mowing higher, and fertilize now with an organic fertilizer in addition to the corn meal for the fungus.