Collection of files resulting from "Process file" element don't show up in "Send Email" attachments field

Hi.

I have this simple BP that has a Guid parameter which represents the Id of a real file inside the system. I take this file into a "Process file" element and tries to save it inside a specific Contact's attachment detail:

Then, in another "Process file" element up next, I take that file created inside the Contact's attachment detail in order to use it in the "Send Email" element:

However, upon checking both the email Activity created from this BP, as well as the Process log for this BP, nothing is attached:

Also, the resulting file collection from the second "Process File" element seems to be empty as well:

What am I doing wrong? I feel like this should work, it's a pretty simple example.

Thanks in advance,

Laurentiu