Until you update the model, this client and server will continue to treat the client as an existing, connected client. Therefore, it won't show up in the New Clients From Server list. In order to make it reappear, you'll want to update the model, and then you should find it in the list of New Clients From Server. To speed up this process, you can restart the client.
Alternatively, you can manually create a new client with the same name as before. Be sure to put the client in a similar group structure as previously, it will add/remove associations accordingly.