I have the same situation in my Tableau Server (German). The customer are using Danish locale in your Excel and Windows. When him publish the workbook, the date changes and create another dates, like 12-01-2018 to 01-12-2018.
Another thing is, exist a bug in Microsoft Excel 2007: https://stackoverflow.com/questions/894805/excel-number-format-what-is-409
So what we are thinking to do is transform the field on Tableau Desktop and publish to see the result.
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