Trying to download the poll responses in .xlsx or .csv format can sometimes result in an error. This issue is caused by the presence of a comma in the poll title which translates into a comma in the associated file name and this is not handled well by Moodle. You can get around this by using Firefox (for now) or simply removing the comma. If you do need to have a comma in the title, you can substitute the html equivalent of the following:
,
This is not an issue that can be fixed on our end so eventually Moodle will need to make an update to solve it.