It is hard to say why this happens unless you provide sample csv or workbook.
Hi Tableau Learner,
I don't think it is possible since Tableau will always accept Integer column as #
I guess you do have couple of records as string within your integer column.
I doubt that because you are using an excel , if it would have been a DB like Oracle then there could have been a different story since data type is predefined there and columns would not allow int value to str variable or vice versa.
I created a simple sample excel as below
I have one different row as 'r' which have made the whole column as String(Abc) whereas the other column is intact as an integer.(#)
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