Check if the http protocol is being used on the slaves nodes.
Also make sure that the web servers on all the nodes use SSL( need not be public facing certs - but name should match the Windchill cluster name used on the LB) as well in addition to the SSL off loading at the LB. A simple test would be to run the windchill wt.auth.Authentication command and check. This is needed for the communication between the nodes themselves.