Comment by ioulian

Ah, I've read what the problem is (90% sure).

Aqara sensors use zigbee, but NOT the full protocol, like Ikea ones for example. So they work fine, until they lose a connection to a router. Zigbee protocol dictates that it will need to try connecting to another router, but aqara does not.

I have a lot of these sensors in my home, normally the connection is fine (5+ years) but sometimes I lose one. Because somebody turned off the lamp (ikea one, acting as a router) (by cutting the electricity to it) by mistake. Then, the connection is lost to that router and it will not try to reconnect.

When the router does not switch, the connection stays. I don't even need to re-pair when changing the batteries!

I've read this somewhere, take it with a grain of salt and validate it yourself if possible.