Client Certificate is not passing through back end hosts

Never going to work. This is a fundamental limitation (and security feature) of SSL/TLS. Upon presenting its certificate, a client also presents information signed with its private key. Therefore any device that terminates (and optionally re-encrypts) between the two end points cannot send the client's certificate because it would never have access to the client's private key. Your options are to either

a) not handle SSL/TLS at the proxy

b) request the client cert at the proxy and find some other information to send to the server