Yeah, this is an issue with the recent openssl updates. It's caused issues across the board for a lot of things, not just QuickBox.
Try this in the meantime.
apt -y install rtorrent. At most, this will install rtorrent with libtorrent 0.13.6 (current) and I have ran this process a few times to fix several installs. After you run the install for rtorrent, send a restart to your users rtorrent service, via the dashboard restart button, or by way of
systemctl restart rtorrent@USERNAMEHERE