I see the following output in the probe GUI when trying to setup the HA probe
<Please see attached file for image>
Since the two hubs have a common hub on your tunnel client, and they communicate with that hub via a tunnel, the HA probe will not work. The two hubs that you wish to set up in an HA configuration must be attachable at least by name services.
The HA probe is designed as a hot-standby system, where a hub will take over all workings (including robots) for a system that goes down. It is not intended as a load balancing solution.