Yellow/Brown/Spotted/Crispy Lower Leaves

I wouldnt worry- Plants do have life cycles and it looks like its the oldest leaves dying back yeah? This is normal, a few leaves dying off here n there is normal and no big deal. Spesh the older bottom leaves. Ur in flower so dont go stupid with the N or you will stop the flowering process- Do the buds look healthy> yes? great- fuck the leaves. lols. Unless you plant to smoke leaves who cares what they do when the plant is in mid flower? Ease back on the n if anything or keep it at a balanced flowering level i.e low and just let the plant do its thing. Most of the oldest leaves will die off before the buds are ready anyways.

I actually think this is burning from too much feeding, not a lack of anything. Cut off the worst leaves, they are ripe for fungal attack and give your plant a rest from feeding for a week or so before resuming with half to three quarters strength nutrients. I have seen quite a few problems with people using the product you are using and it may not be the best thing for cannabis.