looks like you have spilled some feed on there or something buddy I have seen plants in high humidity often show traits like this it could also be a slight imbalance in your ph the plant is still nice and green and growing well I wouldn't worry about it if I were you she will grow loads more fans yet :) best of luck buddy
It is nothing.......nothing to worry about.......it is nothing you did or did not do, it is just a common blemish in cannabis.
Remember......no plant will ever have 100% perfect leaves, 100% of the time.