Hi AgitatedDove14 , thank you for your answer!
At the moment I can't configure both internal/external with the same dns. Before changing the server infrastructure, i'm trying a workaround where I upload the artifact with the internal file server path, and then I upload a string artifact which is the first artifact url where I replace the internal dns with the external dns, and use it to download the artifact from the UI.

Hi LovelyHamster1
That is a good point, I think the safest / robust way is to configure both to use the same dns name/s so both (internal/external) are accessible.
Some background, the URL itself on the artifact is basically a standalone, once registered on the Task, the UI will not replace it but use it as is (The UI has no "understanding" on which server it is, it will just fetch the file).
Are you also using a diff port on the load balancer ?
(because the easiest fix is on your external remote machine to define the hosts file so that the "internal_files_server" is resolved to the external IP (e.g. "11.22.33.44")