Using ProxyCommad to configure jump hosts doesn't work. In .ssh/config I've got an entry like
Host jumptoremote User me HostName remote ProxyCommand ssh firstname.lastname@example.org -W %h:%p
With that, ssh'ing to "jumptoremote" should first connect to login.company.de and from there to "remote" in a transparent way. Note that there is also the ProxyJump command for that since OpenSSH 7.3, but which is not supported by libssh (on the command line both variants work fine).
I'm not using libssh directly but from KDE's Dolphin (KIO) and was asked to report this bug here. See https://bugzilla.suse.com/show_bug.cgi?id=1082703.