Is it single NIC deployment model with NAT enabled ? If yes, pls confirm below settings.
> Exp C is pointing to public IP address or FQDN of Exp E ?
> If pointing to the FQDN of Exp E for TLS, verify the FQDN must resolve to the Public IP
Address of Exp E (for this you need to have a A record in enterprise DNS for it).
If above settings are fine then it must be a network problem, if you can attach diagnostics logs of both C & E with tcp dump enabled then it can be confirmed.
Suresh