A couple of things.
#1. The first picture with the fan leaf that is yellowing, please cut it off. Is is blocking a bud site in the picture.
#2. Day 35 of flower is the start of week 5, this is the time when the buds will start to really bulk up. Week 5 thru 7 are when the buds grow the most. I am not familiar with the fox farm line of nutrients but take a look at the first number on every bottle you are using. This is the percentage of Nitrogen in the solution. Something like Jacks is 2-3-5. Meaning it is 2 percent nitrogen. I use a like called Athena and in bloom it works out to 3.5-3-6. 3 1/2 percent nitrogen. What you are seeing is the plant starting to pull nitrogen (movable nutrient) out of the fan leaves to provide nutrients to the growing buds. It is a little early for that to begin. Try to add a small additional percentage of nitrogen to the next feed. I would probably go 1 to 1 1/2 percent. Only do it one time and see how the fan leaves react. If they just keep yellowing, try upping the percentage to like 2 1/2 percent. If they remain the same go up to 2 percent. If they get really dark green, stop using the additional nitrogen. There is a product call Verde by Humbolt Nutrients that is like 16 percent nitro this is what I use when this happens. Just use small amounts and slow increase if needed. You do not want to add too much because it will cause the plant to physically grow in height.