We have a site with three levels of hubs. In their infrastructure. The Primary & HA are acting as tunnel client and are connecting to two tunnel server hubs which are also acting as tunnel clients toward customer hubs. So tunnel opening is always from inside to outside direction.
Now, when using IM, it depends a bit how we see the env, from the seven hubs there might be some shown as red when logged to one hub, then when logged to other hub all hubs are green. But the biggest issue is that those connections seem to break pretty often, so connections are lost, then after sometime, or restarting those middle level hubs those connections come alive again.
But then it works for some time nice and fine without issues, and then again after some time, those tunnels are broken. When looking hub status in those middle level hubs, they may have lost their connection to primary hubs.