Empty field value showing in webform email content
Similar question was recently answered by the Webform module developer at drupal.org:

"You might just need to append the :clear prefix.

[webform_submission:values:element_value] => [webform_submission:values:element_value:clear]"

https://www.drupal.org/project/webform/issues/2982562

So, in your case use replacement pattern: [webform_submission:values:attach_file:clear]