Why are users reporting missing ticket attachments in Zendesk emails?
Users are reporting missing email attachments is often a result of the user looking at their attachment area in their email client instead of clicking on the links in the email. If you do not include attachments in emails, Zendesk attachments are sent as a clickable HTML link. If the user looks where they would normally see an attached file, they won't see one.
To check if this is the case, open the ticket where this being reporting and select "view original email"
In the original email, you can verify if the attachment was sent:
See Why don't attachment links appear in email notifications? if following these steps do not resolve the issue.