Can a lack of magnesium? Although there may be a chemical burn. What to feed, what is the pH level? What light? Your plant urgently needs help, you lose it, unfortunately. It looks like autumn in Europe.
I get chlorosis like that when my light is too close. It does look like a PH issue, but if you've flushed with PH'd water and already know about that stuff, then I'd say the light is too close. I'm not saying Wendull is wrong either, you got burnt tips and a dark green for too much ferts, but I've seen that go away with by raising the light. A cheap infrared thermometer on the leaf would answer that question pretty quickly.
Sorry you are having problems with your grow. Too many nutrients! Since you are using organic soil and this late in flowering, I wouldn't do anything but give them RO water only. You have enough nutes stored in the leaves and soil to get a decent harvest. I never flush true organic soil! Every time I did, i fucked up my grow! You can still get some sweet buds off those plants.
You might also do well to raise your light a bit because they clearly cant handle the light intensity atm.. they also dont need as much light to ripen up in the final weeks anyway.
I am thinking the Massboost needs lowered and feel like the Peakboost should be stopped Wk 5 and Finaleboost at Wk 7
I think that all 3 should be 1/2 strength max based on chart levels
The Massboost has a ton of Nitrogen and even Finaleboost has a lot for that late in the game
Won’t be pushing anything on them for the rest of this grow but will cut dosages next round
As well I raised light 4inches today but plants were already showing recovery...will drop it back down when they balance as they seemed happy before I even raised it from the flush
Infared read 72F before light raise so unsure if distancing had effect it was 16inches and raised to 20inches on 600w