I'm sorry but it isn't a severe problem as you said, I hope they're going to be fine. I think your analysis is sensible, intellectual, and I agree with you. I think plants are very easily to be burned at flowering stage, and we don't have to feed them every time with heavy fertilizer, such as 800-1000 ppm(1.1-1.4EC), and as my observation, water them with 400 ppm(under 1EC) solution every time maybe proper(I'm using peat-perlite soil mix) , commercial productions' feeding chart is over-fertilized schedule, some said plants will focus on producing flowers at flowering stage so those leaves aren't the point anymore so they are going to be vulnerable.
Thanks for ur advice. Under leaves are burned too, so I guess it is nute burn. And I read a article about PPM&Burn, it said plant will be burned when the water runs off, because water is absorbed faster than the nute of the solution, and the PPM will go up rapidly.