I had a similar issue with the Profit and Loss by Customer report. When I looked at cells that should have values, I found that there was an equals sign before the number: "=341" instead of "341" 

(Subtotals and such had formulas adding together the values in other cells.)

To fix the problem, I inserted a column and then deleted it. This caused Excel to actually calculate the value in the cell, and all the numbers appeared in the spreadsheet.