A. In short, Predicted is an estimate of unique users and Live is the actual number of unique users who have entered the segment. While most of the time the numbers will agree with each other, in some specific cases differences in numbers between these can arise, as the logic between them differs.
You can read more about Predicted and Live Audiences here.
If you have any questions, please contact customer support by email firstname.lastname@example.org or chat with the Customer Operations Team via the LiveChat icon in the bottom right corner of your screen.