Without having watched all the grow steps as they happened, I will throw in my best guesses, but that's all they are, so take them with at cost.

My first thought is that since the younger plant began flower at the same time as the others, it did not have the same root base, so the act of flowering is harder on it. This week make it fade out and finish a little faster than those that we more established and mature.

Second, the plant itself is not the indicator of the bus being ready. I've had strains that had nearly no fan leaves left at the end but the buds were so growing and doing great, while others are still packed with green leaves when the flowers were done. I use a jewelers loop to monitor the trichome color to determine when to pull.

Third, I would cut out any feeding in the last stretch of flower. You want the plant to be done metabolizing those things that will affect the taste. I do water only got the last 2-3 weeks. You end up with a better flavor.

Fourth, shortening or eliminating the day period and reducing the temperatures will send signals to photoperiod plants to wrap it up, but I'm not sure if that will work with autos.

Good luck!