I’ve had similar issues and it came down to a bug in the hub hardware after much debugging. Reported it to ST support and they said they were aware of it and hopefully it’ll be fixed in v2.
The bug is something like this, if there’s a power fluctuation it causes the z-wave module of the hub to stop functioning. The hub appears to be online but no Z-Wave functions work (network and other processing work) but Z-Wave doesn’t, soft reboot/z-wave repair have no effect. The answer is to physically unplug and replug the power cord. Now it works fine. This is a very repeatable scenario and unfortunately the hardware doesn’t seem to handle power fluctuations well. Try it out.