There is a new line in the properties of the iterator, showing the number of locally aggregated rows and that number equals 619255, that should be exactly the number of rows that is missing from the arrow connecting 2 iterators:
1 select 12008353 + 619255
Gives us our perfect 12627608 rows.
Is there any more information on this operation?
Indeed, just right-click on the Columnstore Index Scan and select it’s properties:
This is tied to some columnstore performance improvements in SQL Server 2016.