Those are stress leaves, and here is a perfect example of that. This is a clone that was taken almost 3 weeks into flowering. AFAIK it's nothing to worry about because every one of these that has done this to me have came around and turned into beautiful plants that I've harvested upwards of 2 ounces off of. As for FIMing causing it, I'm not sure about that, I'm sure someone else will be more qualified to help you there, but your leaf growth if it looks like this, is normal for a stressed plant.