Change to Reporting 'Show Summary' option

We have had an existing report in place for years that would sum up the timecard hours by 'reported by' for the previous week.  Within the last couple of weeks, something has changed (we have not modified the report) so that each 'reported by' is showing 0s for their previous week.  If I remove the Show Summary option in the report, I see the timecard details for each 'reported by' and they are not 0.  Why is the 'show summary' option not summing up the hours like it used to?