Heads up, Creators: On Dec 13-14 you may see a noticeable decrease in your sub count as we remove spam subscriptions. If spam is removed, you'll see a YouTube Studio alert: https://goo.gl/qGDBvX This should help give you confidence that the subs you do have are real fans!
Generally, it's normal to see fluctuations in your subscriber count. This is because we want to make sure the numbers are 100% accurate, so we perform additional verification and spam reviews. Also, it's likely folks are subscribing and unsubscribing as well. Hope this helps.