Edit: Nevermind I took the safe route of downloading + installing .568 first.
Definitely glad you took the safe route, it wouldn't have worked otherwise! Every release that stays in the list must be installed in the proper sequence for it to work. However, we remove old releases from the xml file when they are made completely obsolete by newer releases (which we try to do as much as possible, to keep the total number of files to download lower -- but any release that has a lot of content files tends to stick around permanently).
I did get cyberduck downgraded, but it hasn't seemed to help with the S3 issue. I may need to downgrade one version further (I wasn't certain what version I was on, previously), and hopefully that will stop the issue. Either that, or Amazon themselves are having some sort of issue.