Hmmm... I've got one thought, but I'm not convinced it's the answer...
End/start of date range overlap
I think you might see a small amount of different due to overlap at the end of the selected date range e.g. some extra sessions creeping where you have the visit container because of sessions that:
- starts before you date range and end in your date range
- starts in your date range and end after your date range
but you seem to have quite a high percentage different between the numbers, so I'm not convinced that's the explanation.
I think you may need to log a ticket with Adobe unfortunately.
One final random thought... do the numbers change when you refresh the same report? - I once had an issue that caused reports to change between queries/refreshes when it was based on today's data and used a classification