You'll need to explain what you did in a lot more detail.
Where you exporting or saving data to Excel?
What options did you use? Did you select the "group by" option?
The "group by" options is specifically intended to export a single row of data for a group of FileMaker records (the grouping is produced by sorting the records prior to export) so this is the only example I can think of where data would be "collapsed" during export to Excel.