Unsure if this is pm starting or not

You don't have powdery mildew. Your plants look seriously over watered to me. Your plant looks like it's oxygen starved. Saturated soil is not good for Weed. Roots need air or the plant starts doing what i see your plant doing. If you are in 7 gal pots as your diary says, that's way too big for the size those plants are. If you saturate your soil in a large pot with a plant that has a small root mass, you are going to suffocate it. More often than not, less is more with growing weed. Many people love their plants to death. I would let your soil dry out so your pots are light when you lift them. Then water with only 1 liter of a calmag mixture pH to 6.3 Since you are in flowering, drop your humidity to 45% to help get them transpiring at a faster rate to get those pots dried out. Get your fan blowing across the soil surfaces to also help to dry them out. Cultivate the top inch of your soil so it's nice and fluffy and even to help to get some oxygen down to the roots. I'm guessing you have been steadily feeding these plants so there shouldn't be anything lacking, but rather too much fertilizer. Given that i suspect your plants are oxygen starved at the roots, i would suggest holding off on feeding for a week. Get that soil dried out and then lightly water with a calmag solution. Your PPM is pretty high for soil as well. in my opinion 1400ppm is too much. I never go higher than 1200ppm and that is only for weeks 4 and 5 of flower. Then I reduce to 1150, then 1100 and then closing out with the flushing before harvest. You can't run ppm super high without additional co2 injection. Ideally i would say flush your soil with 6.3 pH water to leech the soil of excess salts, but i suspect your plant suffers from saturated soil so now is not the time for that. Try drying out the soil and then lighly water and see if they start bouncing back.