I experienced the same issue with the G410 after a battery change. The doorbell was glowing blue but wouldn’t establish a connection, and the chime display showed blue (as if it were connected). I tried a factory reset, but that didn’t help.
I then removed the batteries from the doorbell for about 15 minutes and also disconnected the power supply to the chime itself (unplugged the USB cable) for 15 minutes. As a precaution, I swapped the Li-ion batteries for alkaline batteries, as these are the recommended type. After that, I re-added the doorbell in the Aqara app, and everything has been working as usual since then. Strangely enough, it’s even working better than before, as I’m now receiving notifications for unknown faces, which never happened previously.
Hello, check the G400 power supply. The power supply may be underpowered even though it has the correct voltage.
Of course it was the G410 that did not connect to the main unity, my G400 unit at my mum’s works seamlessly.
My G410 is only wired. And unfortunately connected to a separate battery powered solar panel, so I would need to disconnect it to see if by chance it reconnects again. Even if the distance is close to 10 meters across one wall, and the fact it needs to directly connect to the chime produces a lot of problems, like if aqara thought all users had the doorbell on the internal wall, when of course the logic position would be at the entrance of the property. SO much so that they developed a most useful G400 seamlessly connecting to the local wifi network, rather than producing a new separate one as for the the G4 and G410.