YEELIGHT 650 - Can't add device in Mi Home | Always goes offline in Yeelight

In Mi Home App (Mainland China), I get an timeout from connecting to WIFI (Channel 2), channel 1 seems working fine. In Yeelight App (All supported regions) I can add the device but after adding it nearly immediately goes offline, if I cut the power and turn it on again I can control it for about 5 seconds and then it’s offline again. Control with remote control works fine.
With this behaviour, I even can’t do any Firmware Update or is there a function to push out the update via Bluetooth?

I come from Germany, if I can do something to help you troubleshooting let me know, I have tried several different combinations (also different WiFi networks already), if I can’t fix this I have to send it back.

Please have a check if the lamp connects to the router when it is offline.

And which type of router do you use?