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!
We perform additional verification and spam reviews to verify the legitimacy of the views on videos posted on your YouTube channel and remove the spam views regularly. This could cause fluctuations in your watch hours. More details: http://goo.gl/S7DIry . Hope this clarifies!