This is because you have added story points values to stories after the sprint has started or you have added new stories to the sprint mid-way. Sprint report will only take into account the story points for the initially committed scope.
A feature request GHS-8776 is already logged to show the actual completed scope rather than the initial committted scope.
A workaround can be to use the burndown chart instead.
Also have a look at the link below and the answers discussion on this topic.
If you spend enough time as a Jira admin - whether you are managing a single, mid-sized instance, a large enterprise one or juggling multiple instances at once - you will eventually find yourself in ...
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