I did a bit of digging because some of my plants have done the same thing. They started to yellow and dry out a bit before they were ready.
I've come to the conclusion that it's a mineral deficiency, specifcially sulpher and magnesium, which plants seem to need alot of during flower.
I used some epsom salts (magnesium sulfate), just a pinch/liter( all natural, unscented) and it seemed to help. I used a little during Veg. just on water days and a little more during flower, just on water days, but not every time you water. Just my thoughts, hope this helps you out a bitππ..
Later!!
@northernMike, that is my thinking too. I did give extra minerals along the way but didnβt seem to do anything on mine. Im so sure its deficiency. thanks ill keep that in mind on next grow