Why do I see different data on a report preview than on the live report?

Environment:

All Sites, Reports

Issue:

When previewing a report in edit mode, the data does not match the data seen when the report is actually opened.

Resolution:

When using the preview function (Ribbon --> View Area --> Views --> Report View) in a report, the replication server will always be used, even if the report is configured to run on the operational database. If replication is behind  this can lead to the data seen when previewing not matching the data seen when viewing the report live.