Hey Growmie,
This happens sometimes, it's like the auto forgets it's an auto and grows like a photoperiod plant, I've had it happen to me a couple of times, the way you can get it to start budding is by changing the light cycle to 12/12 and after a week or so of that you'll notice it beginning to flower. Hopefully, I answered your question and remember ..."Happy Growing" and "Free your mind one puff at a time"