Dude I am going to say this looks more like some sort of deficiency/toxicity more than anything else. Your temps in my view are fine and well within the temps I have grown regularly without problems. Some days here it’s so humid the tent walls are wet. I rarely have issues once I get the fans all working. PH will normally drift as the plants use nutrients and produce exudate from the roots etc but it’s not normally an issue unless it sits outside 5.8- 6.2 for too long. Some additives will buffer better than others, so PH will remain more stable.Some additives I have tried I have abandoned because they cause the PH to fluctuate too much to be able to keep it stable. If this happens then the plant will stress and likely develop deficiencies, which may cause you to over correct and cause nutrient toxicity.
Is your PH pen accurate? Have you tested it against a buffer solution you are certain of?
What I do when I am stumped like this is to revert to a standard time reliable 1.94 grams of MaxiBloom per litre of water, set the PH to 5.8 and give it a few days. Not fancy, but it works. I have never had a serious nutrient deficiency with this dose and know a good number of people who use this ration right the way through. If it’s in veg I will use this mix at half strength via foliar feeding, while just giving the roots straight water with a PH of 5.8. In a few days you will normally be able to tell if it’s a nutrient issue as you will get noticeable green tip growth. Also keep in mind that deficiency/toxicity does not all effect the leaf the same way, as in some deficiencies will damage the leaves and correcting it won’t fix those leaves already damaged. It’s not until the new leaves come through that you can tell. Some deficiencies like Nitrogen for example WILL result in the leaves looking better almost immediately, in this case because higher levels of nitrogen allows for higher rates of synthesis of chlorophyll so the leaves become greener and look healthier etc. Over correction is the obvious risk with this situation.