Invoices IDR are being rejected for some users and not others

Summary:

We have two AP users who have previously been able to forward invoice to our IDR email address just fine. As of recent both can no longer forward, their emails are rejected with "Unsupported Attachment" reasoning in the Invoice Documents Recognition Tracking Report. These same exact emails are able to be forwarded to the IDR email address by other end users and have them completed via IDR successfully.

Content (please ensure you mask any confidential information):

Is there specific settings that you would recommend viewing to determine why the same email is accepted by one user and not the other?