Microsoft Exchange 2013 iApp - Can't login to OWA or ECP if more than one server is active in pool

The solution for the OP was to contact Microsoft and follow their instructions to change the internal URLs to match the CAS server name (instead of the external FQDN). IIRC, they were in a hybrid 2010/2013 deployment, as well.

For Exchange 2013, you don't need persistence for any service, although it shouldn't break anything. Do you certs match between CAS servers? Which version of Exchange are you running?