Just to confirm, have you lost subscribers recently? We've confirmed there are no related technical issues. It's likely folks subscribing and unsubscribing as well. Here's more info: https://goo.gl/6B1Eb6 . Hope this helps clarify.
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.