RESOLUTION: Microsoft has released a fix and an update is available for departments to deploy.
Scanned Attachments Get Stripped When Forwarding Email
ISSUE: In Outlook 2016 for Windows, a document is scanned and emailed as an attachment. If you try to forward the message with the attachment to another user using Outlook 2016, the attachment is stripped off the email message. This is due to a recent Microsoft update.
WORKAROUND: Using Outlook 2016, choose Actions | Resend this message to send the attachment or use OWA (https://office365.uiowa.edu). Microsoft is aware of the issue and is working on a fix.