Highly likely it's grubs especially if that area is especially dry. Grubs like dry, sunny areas of lawn. I put down
grub killer every year in late May/early June that takes care of their "babies" in the fall that eat your roots. Know that this is a long haul fix. If you want to kill them instantly (though with yours the damage is mostly already done for the last year) you have to use a different grub killer.
For you, I would put down new seed and a top dressing right away if you can afford to keep it wet until it germinated and grows a bit. If not, it won't really start recovering until this fall.