A new secondary hub was added in UIM but it is not seen in either the IM or Admin Console.
Communication works bidirectionally (TELNET SUCCEEDS bidirectionally)
Release : 20.3
Component : UIM - HUB
Under hub configure Settings, General tab is Broadcast On. Often this will be disabled to reduce network traffic. Typically this will result in a new hub not showing up.
Go to IM console > primary hub > hub > configure > Name Services > New and add the details for the new hub.
For additional details on these and other settings see the document page: Hub IM Configuration (broadcom.com)