What you're seeing is expected behavior. I'm not 100% sure this will work, but it would be worth trying the Actuator Refresh endpoint to see if that will refresh and update the routes in the registry.
This is something that you can use with Config server, hence it's in the Config server docs, but you might be able to use the Actuator refresh endpoint in this case as well. It seems worth a shot.
https://docs.pivotal.io/spring-cloud-services/3-1/common/config-server/writing-client-applications.html#refresh-client-application-configuration
Hope that helps!