I assume your's is a vApp system.
Can you login to maintenance console, and go to options 3 -> 11, and see what is the hostname it shows. If it sill shows old name, I want you to follow the same step, and change the hostname.
After changing the hostname, you need to reset server ceriticate (option 3 ->10), and reboot the server once (option 3 -> 2).
After doing all these things, reverify the event assignment workflow, and see what server name you are getting.
Regards,
Saravanan