Why are parts of this new lawn dying? (MO, Zone 7a)
I'm in St. Louis, MO (zone 7a) and my neighbor recently laid down seed for a new back yard. He used Scott's Drought Tolerant seed mix, which is a mix of tall fescue and Kentucky bluegrass (see photo). He scraped off the old grass/weeds and soil, added good quality topsoil, seeded the whole yard & covered it with straw, and watered with a timer. The seed germinated and everything looked great for the first few weeks, but now several patches of the new grass are turning brown and dying, and we can't figure out why.
The strange thing is, the dying patches are right in the middle of areas that look great. (see photos) The yard is part sun/part shade and he's been watering it religiously (but not overwatering), and we can't figure out why it's starting to die in random spots. I suspected grubs, but we checked and didn't see any. We did get a few days of rain about a week ago, but I wouldn't think that would be the cause because most of the yard looks great.
Can anyone help us figure out why this might be happening, and what the possible fix might be? TIA.