Why does nobody mention that hens lay weird eggs after a heat wave

So I'm in Phoenix and we had 9 straight days over 105 last month, and my 6 hens went from nice smooth brown eggs to these wrinkled, thin-shelled messes almost overnight. I thought something was really bad, so I called a feed store in Mesa and the guy there told me heat stress does this because the birds pull calcium from their shells to keep cool, plus they eat less when it's that hot. Then he said 4 out of 5 backyard flocks around here see it every summer and nobody warns new keepers. I looked it up in a university poultry guide and yep, there it was in black and white. I've been keeping chickens for 3 summers and only heard about this now. Anyone else in a hot state dealing with this, and did adding crushed oyster shell actually help yours or was it just the cooler nights?