I know I'm lucky, but I've a whole bunch of Xiaomi/Aqara sensors and in the last 3 months (since I've been using and then released my driver ), only one has fallen off. That said, I do have ikea and sm repeaters dotted around to keep things moving smoothly.
The biggest issue I have found that interferes with any of my zigbee sensors is WIFI. Overlapping channels, or very high powered wifi devices can cause my mesh to become reliable. Just today I installed a WIFI repeater as I was having issues with a network device and wanted to boost the signal for it. Nearly crippled my zigbee mesh. I turned the repeater off and everything has settled back down - most likely a channel conflict, but the headache of the zigbee mesh going smelly was greater than the need for the repeater, so I didn't try moving things around.