Currently this is an expected behavior of Export Data in Qlik Sense. The columns are ordered in such a way that Dimension Columns are kept left and Measure Columns are kept right.
Example : If we have Dim1, Meas1, Dim2, Meas2 . The export data column order will be Dim1, Dim2, Meas1, Meas2.
A bug as been reported already, this might be fixed in future releases. Meanwhile you can also refer any extensions which might help you on this issue.