I had same issue, you could try to use setOrgWideEmailAddressId to implement from Address. Because Gmail bounced emails from automated process. You can check it by using:
The problem is that you are trying to add FileType as extension without a dot . previous to it.
Also you need FileExtension property, not FileType, because FileType for .xlsx is EXCEL_X, therefore, you need FileExtension which is xlsx.
So the final result will be:
efa1.setFileName(cversion.title + '.' + ...