Terp1answered grow question 3y ago I think two things are coming together here.
Lack of calcium and potassium.
This happens either when you don't feed the nutrients enough or when these nutrients are blocked due to an excess of another nutrient.
In your case, that could be nitrogen. I would first flush the plants with pH-regulated water and 20% runoff. Then, lightly fertilize again with a light nutrient solution (including CalMag and Bloom).
Happy Gardening 😎