Leech 3.1.4 is out with a couple of fixes. First, certain web servers were accepting URLs that didn’t lead to a file, but didn’t return an error. As a result, Leech would think the download succeeded, yet all you’d see in your Downloads folder was a file whose name ended with .leech—and if you have Leech set to clear successful downloads, it would also vanish from the window. Leech 3.14 is smarter about this, and no longer considers a successful connection the same as a successful download.
The other fix involved a scrolling issue in Mojave where part of the list would disappear on scroll, at least until you resized the window a bit.
Direct customers can update within the app by checking for updates, or by downloading a new copy of the app from the Leech web page. App Store customers should see the update in the App Store app soon, if not already.