Mine seem to be on strike in the heat too - they sit under bushes and take frequent dust baths in the wood ash I put out under the fruit trees in spring, but a good half of them aren't laying regularly and the layers pellets aren't going down to empty in 24 hours after I put them in.
A couple seem to be really suffering, I don't know if there is a health issue with them or simply the heat as they all seem to sprawl around with wings in all directions, laying ones included, whenever I am actually seeing them and the rest are tucked away in every shady corner, the place looks half deserted except when I go out with the corn of an evening..
That said there are one or two I am actively worried about, coming back slowly in the evening by comparison to normal behaviour, and one looks like getting bullied by another when the victim has always been in the top half of hen order and the bully has never shown any aggression previously.. And I don't know if it's heat, hormones, old age changing orders about or something I should be doing something about but don't know what..