This still looks very much like a token issue (online here means that the IP address is pingable as miio device, the config error is if communication is lacking due to the token being wrong)
I would suggest to give the experimental binding a try which receives the token from the cloud… that way you can be sure you have the latest. (as linking to a newer app version, or changing wifi or many other actions can reset the token)
Switch on debugging if needed to see what is the communication between the device to get any meaning full understanding of the issue at hand