A Z-Wave Mesh Network continues to live in your house, even after rebooting the Hub. Just like traditional Routers & Wi-Fi Mesh Networks, sometimes the bottleneck exists within a device other than the main Router. As well, sometimes a Soft Reboot is not enough and a Power-Cycle does the trick.
Take a look at this post, as well as the cautionary posts above, and consider Power-Cycling your entire Z-Wave Network.
With input from @JDRoberts and others, it has been refined to carefully power down & power up either a Limited number of known Z-Wave Circuits, or an Entire House.