Not sure why they leave the network. To me it's looking like Some repeaters just aren't built good or need a Firmware update. Now the Joining the network I see what's going on there. Some of the problem is some people don't know the steps they should be taking to rejoin a network meaning properly reseting a device. From what I've seen though is if you have already had any zigbee device not just hue in the network they will try to automatically pair with the last Zigbee coordinator if it's online. So what happens is the device tries to pair it thinks it paired but the C8 has no clue that it paired meaning it won't show up in your zigbee settings devices. To avoid this make sure the device your pairing is not plugged in or batteries are removed then start pairing on the C8
Here's an example, you'll see the Zigbee device start to pair before I even start the paring process on the C8. Notice the Name changes. 24cd that device thought it was paired before I even tried to pair it and didn't show in the zigbee devices. Also make sure you factory reset the device so it can clear it's zigbee network info.
On the C5/C7 When this happens they seem to be able to handle this kind of thing.
