Been experiencing exactly the same with my last batch of FF premium. Magnesium deficiency/overfed look. I thought i overfed, but after taking some clones and sticking them in more of the same batch... Been 6 weeks, i havent fed once and they are looking borderline overfed.
I think this was just a hot batch of soil.
My grows have been consistent for the last 5 years. In fact i have been reusing my old soil, just reamending with elemental blend. Nothing has changed, except for the new soil i bought.