I would bet money its because of the light, I just had something similar happen. It seems like if it was nutrient related the tops would die instead of growing without chlorophyll. The high humidity could be making the issue worse.
Its good you are getting a dehumidifier even if it isn't the cause, that high can issues when they are flowering. If you can get around 30-40% you will get a lot tighter nug. They do raise temps so be ready for that also.
Talk about foot in my mouth, I was bitching that everyone keeps their double endeds too far away; and I now have a clone with a bleach spot on top of its top bud because it stretched above the other clones about 8 inches. It looks the same color as the issue on your plants. So instead of recommending 3 feet from the canopy I now recommend four lmao. Not sure why it wasn't an issue before this season either, especially with having better grow conditions now.
I have to continue working so I can get this day over with, let me know how the new growth looks. Air flow really helps the plants fight humidity also. Most air conditioners will bring the humidity down to 50% on top of fighting the heat.