Hi Jonathan
Looks like the application error does go through the fault mapping as expected.
To be honest, I'm running out of ideas for this, but let's try the following.
Have you tried getting the response message payload from the monitor, and manually executing the fault message mapping in ESR mapping Test function? Can you check that the output after execution of fault mapping matches exactly (structure and namespace) of your sender proxy service interface's fault message?
Rgds
Eng Swee