As well as the physical value, this report will also take into account orders pending in the Dimensions/Delta process. If an order is stuck, this may create a false positive in the report. Please check your Delta import batch, and ensure everything is up to date.
If your report is still showing a different physical value compared to what shows in Dimensions, Support will need to investigate this further and possibly run some scripts on the database. Therefore please raise a new case online and reference the title of this article and please include details of the stock code affected and the quantities seen.