From the homepage (https://winscp.net/eng/index.php) I click the "Go To Download Page" link under the 5.1.3 release, and it takes me to the "Downloads" page, but that page only as releases up to 5.1.2. I'm downloading 5.1.2 for now, but would like the most recent update if it is in fact available.
Apologies if this isn't the correct place to post a site issue.
So odd... I just went back and it looks fine to me, too. Before it said '5.1.2' instead of '5.1.3' at the top, but I didn't take a screenshot at the time. Oh well, guess there's not a problem after all.