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, sub count fluctuations are normal. While we remove spam subscribers regularly from your channel, it's likely folks subscribing and unsubscribing as well. Here's more info: https://goo.gl/6B1Eb6 . Hope this helps clarify!