You have a buddy with the same problem: Need help troubleshooting z-wave intermittent non responsiveness
Here is what I suggested over there:
There have been a couple of cases with sensor devices for some reason crashing the zwave on the hub. If you have any sensors turn on logging if not on already and then around the time the zwave crashes check the logs to see if there is a pattern of a certain device reporting in right before the crash.
Also, please look through my pinned post I linked to above, there are a bunch questions in there as well as info requested when asking for help with Zwave such as the zwave details page, etc... please provide all that info.
There are steps in there to do a backup/restore which cleans up the database, I would recommend that as well.
