Stelpro Z Wave thermostat fails after a while

I recently got a Stelpro Z Wave line-level thermostat, and an Aeotec gen 5 z wave stick to communicate with it. Initially, when I set it up, everything worked as expected and it was actually surprisingly simple to get things configured.

However, after running for a while, eventually the thermostat doesn’t communicate with Home Assistant any more. This is my first z wave device, so I’m not sure how to troubleshoot in order to resolve it. I know that the node is showing as “failed” in the info box, and trying to run “test network” or “heal network” doesn’t appear to fix it.

The only way I’ve been able to remedy the situation is to manually put the z wave stick into remove mode by holding the button for a while, then removing the thermostat from the network. Then I need to restart the network and re-add the thermostat, which is a huge hassle.

How can I troubleshoot this? I’m very confused why the node keeps appearing as “dead” and why I can’t test, heal or remove the node using the UI. Overall, I’m pretty frustrated with how difficult it is to recover from this state - I need to delete the entire z wave integration and start over!