Well what should happen is that when OWA initializes and reads the hidden message in a users mailbox, it should determine the EV server it has to go to from that message.
If it's going to the old EV server, then its possible you haven't synchronized the users in the new environment yet.
Also you may want to amend the EVServers.txt on the OWA server and re-run the configuration script so it can update the proxy configuration list
https://www.linkedin.com/in/alex-allen-turl-07370146