The Release Burndown report return completed issues on the incorrect Sprint if the issues were finished during a Sprint they are not added too.
The same applies to Epic Burndown report
Also, The Release Burndown will show the issue under the latest started sprint by the time the issue was completed.
- Create a release (ABC) and two Sprints (123 and 789)
- Create a new issue TEST-123 and add it to the Sprint 123 in the release ABC
- Start the Sprint 123
- Finish the Sprint 123 and move the open issue to the Backlog or don't fill resolution field
- Start the sprint 789 with different issues (Don't add the Issue TEST-123)
- Close the issue TEST-123 (Adding its resolution)
- Complete the Sprint 789
- Navigate to the Release BurnDown Report and select the release ABC
There should be a note mentioning the issue was not part of the sprint.
Or the correct sprint should be listed and a note informing the issue was completed after the sprint.