I suggest to add more mains-powered router devices to increase the robustness of your Zigbee network. I see that you have only 3 router devices that service most of the battery-powered devices.
If you're not against using community apps, you can try the [RELEASE] Zigbee Map app to get a better picture of your network. Maybe it will help to better investigate the problem. Disclaimer: I'm the developer of that app.
