When placeholder files are created, metadata containing the recall URL is written to them. This URL contains the name of the EV server at that time. If the name of the EV server later changes, this metadata is not updated. Therefore, the placeholder recalls will attempt to contact the old EV server.
A simple solution is to update the hosts file on the file server to redirect requests for the old EV server name to the new EV server.
Another solution, which is more complex, is to recreate all placeholders using FSAUtility's -c option.