If i remeber correctly, chrooting in ispconfig 2 requires a recompiled and patched ssh daemon. These patches are not available anymore for recent sshd versions as the maintainer stopped the development a few years ago, for that reason ssh chroot in ispconfig 2 is not working anymore on recent linux distributions. ISPConfig 2 itself is not under developmenet anymore too since the new ispconfig version (ispconfig 3) is available and stable. So ispconfig 2 wont get updates anymore.
You should really consider to use a ispconfig 3 setup on your server, its much more powerfull, easier to install and has full chroot support for ssh users and many more, is actively supported and gets bugfixes and new features.