Browning spots on lawn

I live in Massachusetts. We’ve been below average temps for most of spring until recently. My lawn looked flawless and I have to mow twice per week. And then on my last mow I noticed brown patches after my mow. Not completely dead spots. But what appears to be light browning. When I look closer I see some grass blades appear to be dying. I fertilized with Milorganite last month and just last week put down some lime with iron. What is this??

View attachment 361725 ...

Browning spots on lawn