When using the File Download button option on a form confirmation dialog, the button points to a URL which includes the form fields as parameters (i.e. http://sub.domain.com/page-title/a-fo…#). Is there a way to disable the parameters from being added to the File Download button?
Are you hosting your file on Unbounce and using the built-in “Download File” option  or are you hosting your file elsewhere and linking it through the button ?
Based on your description, I assume you are using the button to link to a file hosted somewhere else.
Please check that you haven’t accidently ticked the box “Pass through URL parameters”