@Carl Endres 

It works fine for me.  Don't apply any filters.  The fact that you're referencing 'Paid Through' indicates you're applying a filter.   Click 'Customize' and change the date range on the 'Display' tab.  Any time I change the date range, it changes the average days to pay for every customer as one line item per customer.  Just run the Average Days To Pay Summary report and change the date range.  No filters required.