Looking into the available logs with Alarm.com, it still appears to correlate with Z-wave. The only correlation and possible instigation we are seeing is that this seems to occur following a modem ping, which in turn follows a previously sent list of Z-wave commands (often schedule edits)
In both cases you just mentioned we are seeing a few Z-wave commands start to hang earlier prior to the reboot.
If this is indeed a type of buffer issue related to Z-wave, there may already be a fix for it. 2GIG firmware 1.17 includes support for Z-wave command queuing, which will help the module process the commands in sequence.
1.17 is available for OTA and this account has a Go!Bridge, so we could apply it if you would like. Please confirm if you would like us to go ahead and send that.