I had the same problem.
I solved reducing the feeding so, lowering the EC. Try to reach a PH of 6.2/6.3.
Raise the light or decrease his potency and wait 2/3 days. The plant will recover easily.
Be careful now, youre in flowering and there is no space for mistakes. A good tips could be to do a little flush with ph water only, but do it only if you'are sure that the soil will dry in not more than 4 days.