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!
Sounds like an excuse to mass delete peoples' subscriptions to me. But then, they've been doing this for many years, starting when Google took over and forced that asinine Google+ down everybody's throats.