While trying to check a segment in the test section, I arrive with a different volume when I test in the top part and the bottom part. Why are the subscribed volumes different?

Answer:

There is a difference because the first test (the top part) establishes the volume according to the active subscribers.

The second test, (the bottom part) tests the segment on a sample of 10 / 100 / 1000 contacts, which includes inactive and unsubscribers.