Interesting. Hop 18 is not a routable IP address. This looks like an asynchronous route, given what is happening at hop 17.
Simply put, the packet loss happens as the route back is not the same as the route to it. 100% packet loss is, when the network is working, is always an asynchrnous route.
It is a limitation of the way a traceroute works as they can only trace synchrnous routes.