Hi Nicky,
What's your BW version? Is it BW 740? If so, you may check KBA 2040023.
As per this KBA, there is a bug of BW 740. In the back-end, you will see the records with empty values in BPC dimension. For example,
DimA DimB DimC SignnedData
A1 B1 C1 100
A2 B2 200.
Then, the 2nd record will be missing from EPM Add-in report as the no records in DimC.
As a solution, you may try to apply BW note 2035451.
Best Regards,
Charlie