At this point, I have 2 in the living room, 2 in the bedroom, 1 in the kitchen, 1 on the landing, 1 in the spare room and one in the store room. They have never once gone unavailable for me. But I have 2 Zigbee bulbs and an RGB+CCT Zigbee LED strip in the same room as the Pi with the Conbee2 stick. Looking at the Zigbee Map on Zigbee2MQTT, it’s quite obvious that even the sensor just 20cm away from the Pi, is routed through a lightbulb rather than talking to the stick directly. It seems that sensors prefer to find a mains powered router. I even have a Lux sensor outside that happily manages to route back to the stick, despite there being 3-6ft thick stone walls on it’s route.