This could be your problem. Have you ever heard about toxic salts buildup, TSB? Constant high levels of nutes build up over time in the leaves where the plant stores the excess until it gets so high the leaves start burning all across their surface. They go all yellow/brown/orange and feel all thick and crispy. This doesn't show up usually until about mid-flower and even with serious flushing will not stop progressing until it even affects teh tiny bud leaves near the end of flowering.
I know with the pH perfect stuff 1ml/L is almost 300ppm. The JJ is going to be even higher than that. Like I mentioned earlier I rarely went over 2ml/L unless whatever strain was showing signs of needing more then I might just feed 3ml/L every 2nd or 3rd watering but stay at 2ml/L between the higher doses. A week before flipping to flower I would feed extra Bloom and a half dose of Big Bud to 'prime the pump' just before flowering. Fast bud development and lots more bud sites than waiting to add the bloom booster 3 weeks into flower like a lot of peeps still say to do.
The stretch period is a huge growth spurt so all the nutrients should be present in higher doses. I will add extra light, set my exhaust fan to wait until it hits 90F before kicking in and light up my alcohol lamp to add lots of extra CO2 for the stretch period only. Amazing growth and ping-pong ball sized buds by the end of the stretch. I used to monitor the ppm drop in my DWC grows and noticed up to 4X the drop during the stretch but returning to normal feed rates as soon as stretch was over. Maintaining high feed levels after the stretch especially with extra P is a great way to get that 'chem' taste in your buds. Less P but more K after the stretch with extra Mg and S is the way I play and I grew my first buds in '78 so have tried almost every style of feeding imaginable in that time. Yes I am an old fart and will be 69 this Oct.
When starting my seedlings/clones I use 1ml/L of each so a 1:1:1 ratio of Grow/:Micro:Bloom. Once rapid growth is established I switch to a 3:2:1 ratio then go back to 1:1:1 a week before flipping with the added half dose of BB. Once stretch is over then switch to Lucas which is a 0:1:2 ratio. I have straight K so will boost a bit with that about the 6th week and up the dose of Epsom too. I'll lower the ppm levels to just straight water with maybe a small dash of K and Epsom the last couple weeks. I want to see lower fan leaves going yellow and limp the last couple weeks so I know the plant is having to steal some N near the end and there are no signs of the dreaded Toxic Salts Buildup.