Thanks for reaching out.. Are you seeing this on YouTube Analytics or through a third party app? It's possible that this is due to the changes in sub count. More info here: http://yt.be/help/abbrev-count …
Subscriber fluctuations are normal whether channels are hidden or not. In addition to user subscribes and unsubscribes, YouTube adjusts subscriber counts around the clock to remove any inactive or illegitimate subscriptions. More info here: https://yt.be/help/qF2u