When an IM ticket is created via an EM ticket that contains an attachment, the attachment does not exist on the IM ticket. When the workers of the IM ticket click on the EM ticket through attached processes, they can see that an attachment exists but they do not have permissions to view this attachment.
No errors are thrown, but the attachment does not get associated with the new IM ticket.
The solution to this problem is to modify the SD.Email.InboundManagement Workflow to attach the document(s) to the incident at the time they're created. To do that, use the following steps: