JAX-RPC webservices created in 10.3.1 responses are different after recreating in 12c

When we upgraded from 10.3.1 to 12c, we followed the instructions to move our JAX-RPC webservice to 12c. But some of our client's requests are not accepted by 12c and some of our clients cannot consume the response from 12c without coding changes. Due to circumstances out of our control, we could not make our clients change their software (Some say they will stop buying our product if they have to change and we are talking about tens of thousands of customers.). So we had to stand up a small 10.3.1 instance to just handle our JAX-RPC webservices (all work