Not to discredit the other opinions but you said you use FF BB and TB right? The FF feed schedule actually calls for grow big in flowering as well, just a 2 week break from it when you switch the light cycle. That leads me to believe you may just be getting Nitrogen deficiency.
Nonetheless, you are 7 weeks in flower and dont need those fan leaves, they are going to yellow and fall off during flower, its perfectly normal. That being said, its too late to correct a N def, but who cares, you're home free. I would start your two week flush now.
And chances are the yellowing will continue until harvest, but again its perfectly normal during the end of flower to get that.
Good job getting to harvest.
Again I dont mean to discredit the other posters, they are probably right, but I did the same thing with FF nutes, forgot to keep adding grow big in flower and looked just like that.