Aqara Zigbee devices are renowned for having a longer keepalive check-in period than many routers expect. So when they don’t check in on time, the router marks it as dead. Often, a quick tap of the setup button to re-announce it to its router will cause those routers to “unmark” it as dead—you don’t need to re-pair it. But it’s frustrating enough when it happens.

I have a handful of Aqara sensors that constantly dropped away, so I just flashed an XBee with router firmware and have it on a small USB battery that stays plugged in. That way power outages won’t cause issues with the “leave and rejoin” request that routers will issue to aged-out devices, which my Aqara devices seem to balk at.