When you create a Custom Report which includes metrics such as Unique Visitors or Unique Users, you may see the following message in your custom report:
No data is shown because this report only contains metrics that are not supported by the selected period (Unique visitors)
This message explains that the “Unique Visitors” metric (which is included in this custom report) cannot be processed by Matomo. Processing Unique metrics (such as unique visitors, unique users, etc.) will only work for Custom Reports when the selected period is Day. When you select any other period such as week, month, year, custom date range, then the custom report will not include the Unique metrics. (We are currently not able to process unique metric values for these periods because of performance reasons.)
To ensure that your custom report will always show some data, we suggest you also add the “Visits” metric to your custom report as well as the Unique Visitors or Unique users.