Archiving your results prevents them from showing up in both your main Question History page and your Scoresheet. Archiving is a way of hiding your results without fully deleting them.
To archive your results, go to your Question History, select the menu button on the report you'd like to archive, and select "Archive".
To view the results you have archived, select the "Archived Reports" check-box on the left-hand side of the page. That will toggle your results between Archived and Unarchived.
To Unarchive a report, check the Archived toggle so that you're viewing all the Archived results. Then select the menu button on the report you want and select "Unarchive".
If you are missing results in your Scoresheet, check your Question History as described above, to make sure they have not been Archived.