I had similar things happened to my freshly planted Kentucky Bluegrass in a couple areas. What started out looking like dollar spot spread larger and larger dying off. I knew I didn't have many pest so I figured it was a disease like snow mold even though it never snows here. The baby grass was pretty wet sense November of last year. I used propiconazole it seems to have stopped it in its tracks and just now recovering. I'm sure some more experienced people may ring in here.