Looking at your screen cap - you do have a lot of (I assume) MS6's - for me these have been problematic - they just didn't seem to make good repeaters - the ones on usb I mean. To be fair others have had better luck. I like Zigbee sensors as they are a bit faster.
The other thing to consider is memory consumption.. My C5 "Cloud and Network" hub shows a gradual decline in free memory and I have to reboot after it gets too low. Consider adding a watchdog app that can reboot your hub in a controlled fashion rather than being forced to do it when things stop working. Here is a pic of my hubs - notice my Network C5 is already in decline even after a reboot yesterday evening. I suspect my Flume water monitor driver - something I've done with the configuration not sure.
Your Zigbee devices need to be in range of each other, the frequency of their signal is higher (2.4 GHz) so WiFi can cause interference and the signal does not propagate as far as Z-Wave. I use channel 15 to try and avoid WiFi interference. Zigbee seems better then Z-Wave at adapting to changing situations though.
Lastly I would consider not running a Z-Wave repair all the time. Z-Wave+ generally has the ability to adjust but it seems to take a while - few days to weeks.
