This is often the result of one or both of two issues. For starters it is not uncommon for there to be a delay between the information available from YouTube to TubeBuddy. But also YouTube has a tendency of going back and reviewing their numbers before re-releasing them. For example, you will have days when you gain three or four times the number of subs that you normally do. The next day you'll lose a quarter of those, only to gain them back a few days later. This is YouTube reviewing data (they do the same with views, watch time etc). So data may be caught up in a lag between YouTube and TubeBuddy, or that data may be under YT review.