After reading the response you received from support and knowing enough about Tableau Server to be dangerous, it is the Export of the excel spreadsheet that is causing problems. You have to connect 'live' to the spreadsheet.
- Leaving the export as the connected data source, connect to the spreadsheet. Make it a live connection.
- Replace your data source (from the extract to the live spreadsheet. In the Data option on the menu).
As long as the spreadsheet retains the same name and the location that the spreadsheet is stored is accessible to the Tableau workbook, you should be good to go.