If it works with a binding to a physical or sub interface, but not with a loopback you likely don’t have routing setup to work with the loopback interface. Why do you want to use a loopback interface instead of an actual interface?
That has nothing to do with bindings for SIP or SCCP, so what other services on the router is using is irrelevant to the question you ask.
Do a debug ccsip message and debug voip ccapi inout on both of your CME and post the output in two separate text files, one per router, that you attach to your response. Please outline the calling and called numbers and time of the call so that we can easily pick it out in the shared output. Also please share the running configuration from both routers, in another set of attached text files, so we can validate your configuration.
