Oh, ok. I've misread your initial post. I've understood that the connection breaks during file transfer. If it breaks while idle, then indeed the keeplives are the way to go.
https://winscp.net/eng/docs/ui_login_connection#keepalives

It sends dummy packets to the server just to keep the connection alive :)

@Zangenesel: Oh wow, dude, I think you did it. Thanks! I think it's working now.

So what was that setting doing?

This may help.

That setting doesn't help. I just tried it.

And no, I did not try other client. I got used to using yours.

Is there a log or something that I can enable to see what is the cause of the timeout?

Try turning off Optimize connection buffer size:
https://winscp.net/eng/docs/ui_login_connection

Did you try other SFTP client?

This really drives me nuts. I'm currently traveling through Kenya and I needed to update my website. I haven't used WinSCP for while, so I had to download a new version on to my laptop.

So after I have configured it (using SFTP), for some reason, it times out after about a minute. So when I drag a file to upload to my site it first shows this window:


The shows "Copying files to remote side failed":


and then connecting again:


Then it works for about a minute and if I don't upload anything, it goes back to the same sequence as I showed above.

My website is hosted with DreamHost. I contacted them first, and after looking at my IP trace their support guy told me that some of my packets never reach their servers. He then suggested trying a different SFTP client.

I don't have any problem using the internet. I have a 100Mbps connection here.

Why is WinSCP disconnecting and showing that window all the time?