This happens when either you manually unfollow users that the bot followed or if a tool that you are currently using unfollows users that our bot automatically unfollows.
The reason why this happens is because our bot cannot detect any actions performed by outside sources such as users manually unfollowing accounts or if another tool did it. When our bot goes and performs the automatic unfollow it will flag any user that is unfollowed during the time it last performed the same task and the current task and mark every user that has been unfollowed regardless of who or what actually performed the task and report it to as our bot unfollowed the said user. This will result in a difference in your analytics over your overall follows and unfollows.
If you find this to be problematic, we suggest you do not manually unfollow users that our bot followed.