Did you know there are two "end dates" of a sprint according to Jira?
There is the Planned Date (the date the sprint is planned to finish) and the date the sprint is actually completed (by the person closing the sprint).
The table below shows the correlation between Jira and Plandek.
Complete Sprint (button in active sprint view)
As an admin user you can decide which date you'd like Plandek to use for the sprint metrics. This changes the default for all sprint based metrics.
Simply toggle between the two option and when you have decided, click Save Changes
Remember you can also change this at a metric level by going in to the calculation on the right hand side in metric settings for that specific metric.