its just what happens to some peppers in 90+ weather with full sun.
annums are particularly vulnerable in my experience. i had several annums that basically stunt completely... pretty bad wilting, growth became distorted all flowers failed. i just cut them down because they got to be farily ugly plants. these were greenhouse bells.
annums like the hatch type chilies...big jims etc do ok vegatativly, but the production comes to a screeching hault in the hot houston summer.
chins, though not all chins, seem to hate the heat too... partial wilting and fairly sever stunting and pretty much total loss of all flowers. chins do seem to put up with it though... they will continue to grow out vegatativly, so if you can deal with the months of non productivity, in the cooler fall months you will have a larger plant... hopefully with a larger root system ready to pump out pods for a few months.
not all chins though... the most productive chin i ever grew was the congo red. It was like i was growing a giant cloud of pods with some leaves and twigs thrown in here and there...
its production slows and the pods become misshapen in the heat... it even wilts partially... HOWEVER, it keeps pumping pods out.
why?
no clue. we can only guess that some chins are better at setting fuits in the heat than others. id love to hear from a plant scientist on this issue...
frutenses seemed to me to do the best in full blast sun... bacts seem to do well too.
my tobasco plants seemed to care very little about the heat. the growth of the plant it self slowed down noticeably though, just not the pod production.
all just experience though.
ill tell you though, when i first put up my shade cloth, it was like a night and day difference. its worth your money and time and effort i assure you... if you can pull it off i encourage you to do so.