Customer complains a data mismatch in the report. The reports shows a different data when accessed from the reports menu, but the same report when configured for dashboard access to some users gives a different / limited data. What could be the issue?

Customer should have configured context filters in the report configuration. If the reports are viewed from dashboard / widgets, the context filters for e.g., if Submitter / Owner option is selected will show only the tickets which are submitted / owned by the technician i.e., based on the logged in user/technician. However, such reports when accessed from reports menu will show all the data. This is how the context filters works and it is applicable only for the reports which are configured for dashboard / widget access