Are you monitoring the temp in the coop?Is the most common time of heat stroke death at night when they are inside the coop? My flock free ranges and only goes in the coop to sleep. My coop has 4 windows and lots of eaves ventilation, but from what I've been seeing from my other chicken friends is finding dead birds in broad daylight.
I'm going to hope that you all are right and my birds are going to be okay. I'm going to hope that all these people posting on facebook and other forums finding their birds dying of heat stroke are exaggerating. I'm going to hope that global climate change isn't affecting my area at all and that this is all just normal stuff, in the face of all evidence to the contrary. I'm going to cross my fingers for the next 10 years and hope that I do everything right for them. The more I grow to love them for how wonderful and special they are, the stronger my anxiety over their welfare. I can't seem to stop myself from growing attached.
My birds are picky and I can't get them to eat anything that isn't mealworms, grubs or fried eggs. I tried frozen treats and they won't try them or if they do they violently shake their heads and leave the treats. Frozen peas, watermelon, honeydew, blueberries, I don't think they like the cold in their mouth. My older birds are handling the weather much better than my babies who are too stupid to not stand in the sun. They have a tendency to haunt my back step, because I go out that door; my step is aluminum so I am throwing ice cubes down on it. It seems to be helping them. The ice cools the metal they're standing on and they peck at the cold dripping water. I have four watering stations where they range and one of them is a great big huge open bowl so they can walk into it if they like to and some of them do, I change the big bowl every hour with fresh cold water.
Can you set up a fan to blow cooler air into the coop late in the day to help cool it off?
Have you given them some electrolytes?
Made a big chunk of ice to set into a shallow pan?
These things really help here, especially the EL.
The ice block pan you may have to show them how at first,
but once one of them 'gets it' the rest will follow.
https://www.backyardchickens.com/articles/aarts-extreme-weather-spiel.75893/
You can set up an air conditioner in the coop if you want,
most of use can't afford that type of luxury....I don't even have AC in my house.