Unfortunately I don't have an answer for you. Though I am wondering what the air temp at the plants is. I have a feeling if you think it might be an issue, it probably is to high (even if it is not the problem). I would vent the heat out to eliminate it as an issue anyway. Pepper plants like warm climates but I wouldn't want the temp to get much above 80 degrees. I also would make sure the
nutrient solution's temp was between 68 and 72 degrees consistently. Then check the pH level daily and change the nutrient solution once a week at least until they were looking healthy. These things I would just do anyway, I don't know if it will solve the problem but it should eliminate them as a problem.