I had the same problem over the past several months since late April. Kept troubleshooting idea after idea. Ended up figuring out my problem. Dont go by everything you read online suggesting how what and when to feed.
The problem ended up being underfeeding at 900 ppms as suggested. Lost 2 girls due to this problem before correcting it. My veg gets between 1000 and 1300ppms using GH 3 part solution with only diamond nectar additive. Bloom gets 1500ppm. They are doing awesome. So depending on the strain, depending on the type of water you use(Ro or Hard), as well as differences in different hard water properties, and depending on what brand of nutrient solution as well as is it organic or non organic all will play a part in how much you need to feed.
And i might add also humidity plays a role also in nute strength intake also by how fast and easily the leaves can transpire the toxins. Higher humidity can cause lockout due to lack of ability to transpire. And also the intensity of the light will affect intake.
