To clarify, different pages across YouTube (such as the logged in homepage, search & watch pages) are updated at different intervals. It is a common occurrence that the total subs count may vary on these pages at the same time. Hope this helps.
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!