Just wanted to share my recent experience regarding a sudden unresponsive Z-Wave network.
My stick was plugged straight into my PCs USB 2.0 port (not a RPi) and has been up and running for 3+ years. About a week ago, after adding 2 new nodes, I experienced bad performance and eventually a total network failure. My Z-Wave sniffer showed no communication from the controller and the LED on the stick was stuck on a solid blue.
After trying a OH3 downgrade from a recent snapshot to M3, other USB ports and even replacing the stick, all to no avail, the problem turned out to be power related.
After moving the stick over to a powered USB HUB, it has been blinking merrily ever since.
So, either my PC HW power-feed ability has deteriorated or it has always been marginal and adding 2 more nodes pushed it over the edge.