I have encountered a similar issue attaching CSV files in v1.17.3 - it appears to be caused by the new "Make sure mime type is valid" check added to isValidFile in class.forms.php - FileObject::mime_type($file['tmp_name']) is returning 'application/csv' but $file['type'] returns 'text/csv' so the function returns false, causing the Invalid File error to be returned
Using Apache/2.4.52 with PHP 8.0.24