Are you following what their feed chart says, more or less? And this is being feed every time, no water only days? None of the other components to their system? If not, I wonder if you're getting short on micronutes maybe,.. plenty of N going in, P seems OK....
Those lower leaves are normal fade, no worries there,...
Cut out the Grow part, stay on Bloom; on the worse two plants, skip feeding every time, water only and see if the symptoms halt,... gonna be a few-several days...