Windows – How to connect to an FTP site in Windows Explorer

Based on this:

ftps://username@1029.56.34.19

you are using FTPS. There is FTP, SFTP, and FTPS. Furthermore, there are two types of FTPS - implicit and explicit.

FTPS is FTP over SSL (like HTTPS). SFTP is really a form of SSH (behind the scenes an SFTP client is logging in via SSH and issuing commands).

The easiest thing for you to recommend your third party to do is to install Filezilla and then give them the URL. Alternatively you can look into FileZilla's import/export functions which may be easier for both you and the client. WinSCP will also work.

Windows does not have native FTPS or SFTP support. Just the weird way it integrates with Windows Explorer (not Internet Explorer) and the old ftp command.

Due to its architecture the FTP protocol does not work very well in environments making use of NAT. NAT is heavily used in mobile networks and the used helper applications are sometimes buggy, which might explain the difference you see. There might be other reasons while it fails in one network but succeeds in the other but without having lots of details about the networks all is speculation.

I strongly recommend to move away from FTP and instead use SFTP, that is file transfer over SSH. FileZilla supports SFTP but you need an SSH server setup at the server side. But don't confuse SFTP with FTPS which is FTP with TLS and has even more problems in environments using NAT.