In my home every 2 weeks they enter in this modus. It happens because my wall switches are very old.
It’s a pity that so far I didn’t found a way to disable this 3 on/off reset. Anyways it’s very easy with the Mesh app to make them join your network again.
Note: For concrete lamps you need to get it out to make a successful Bluetooth connection. It seems WiFi passes through cement but Bluetooth not so good.