This is another issue where there are many inconsistencies in Jira's Reports section.
Steps to Reproduce:
View any completed Sprint in the "Sprint Report" section of the Reports tab.
Under the "Completed Issues" section at the top of the Status Report, view the Story Points completed number on the right hand side.
Above that number, click the blue hyperlink "View in Issue Navigator"
On the Issue Navigaor screen choose to Export the report to Excel
Sum the story points in the Done column of the report.
They will NOT match up the Sprint Report completed points.

This happens to all of my Sprints that have any scope changes after the Sprint begins: Eg. stories are added or taken away, there are sizing changes, etc
There is no consistent apples to apples comparison amongst the reporting screens, even within one reporting screen.
Can you reproduce this error on your end? Thank you.