Don't stress the thin egg. Sometimes, it just happens. From my reading recently, it appears that it occurs more often during summer, where they are all hotter. The temperatures have added enough extra stress to their poor little bodies that things just don't come out right sometimes. I've had my first two soft-shelled eggs this month as well, and my girls are all fed very well, too.
How many hens versus eggs do you have every day? The last week, I've been getting a single egg out of my two layers, except yesterday. The hen we had to break of being broody hasn't started laying again, so we're down that egg as well. It's been my lowest collection week since our girls started laying.