In our case we were getting UnmarshalException because a wrong Java package was specified in the following. The issue was resolved once the right package was in place:
@Bean
public Unmarshaller tmsUnmarshaller() {
final Jaxb2Marshaller jaxb2Marshaller = new Jaxb2Marshaller();
jaxb2Marshaller
.setPackagesToScan("java.package.to.generated.java.classes.for.xsd");
return jaxb2Marshaller;
}