SSRS 2008 to 2014 Migration Excel Export error
This appears to be related to some implicit conversions that are occurring in the background when exporting the report to xlsx.  Numeric columns are being sent to excel as if they are text columns.  One report responded to a change to the query using an Explicit cast to Numeric (Cast as opposed to convert to remove any commas or other formatting that might confuse the conversion).  Several other reports did not respond to the Cast but returned correctly after using an expression conversion of VAL().  I still have several reports that are not responding to either.  If anyone out there has a good explanation for this I'd love to hear it.