Hi nolien,
Let me help
you correctly export your report to excel.
This might have something to do with the setup of your excel application. You
can update it to the latest version.
If the same thing happens, you can contact Microsoft Support Team through this
link, just scroll down to connect with an expert: https://support.office.com/en-us/excel
Drop a comment and let us know if you need have any other questions. We're
always right here to help.