The C-4 has some Z-wave and local devices (eg: Onkyo). The Zigbee radio died on this hub and the devices were moved to the C-7. The C-5 is Zigbee only for lighting (Sylvania and Sengled). The C-7 is Zigbee and Z-wave originally to replace the C-4. These have been working for years. The C-8 is new and destined to cleanup and replace the other hubs. It only has three Zigbee devices currently.
Tonight I tried to setup Hub Mesh on the C-8, but none of the other hubs are showing up.
You can see the C-8 doesn’t see any hubs and the other hubs don’t see it. I’m not too worried about the null IP on the C-4 as that one has the bad radio and will be decommissioned once I get devices moved.
One idea, though this shouldn't matter (but can't hurt and has made at least reconnection faster for some users):
Under Settings > Hub Details, what is Hub name on LAN set to? Try setting this to something unique for each hub. (Note that this is not the regular "Hub name" field, and it is only available on 2.3.6 or later--and it's worth noting that any hub running this version means the other hubs should be, too.)
Hmm, suddenly everything is working today. Perhaps the name changed needed time to sort itself out. I’m not concerned with the failure on the C-4 as that one will be decommissioned. Currently it is running some local integrations with Alexa. That’s working fine and will get ported eventually.