@Anton L.Z. "adding new Deco" in my post includes "reset" and "wait for flashing blue". "Fails" means "configuration fails". Have tried also - to connect this deflect Deco directly as stand-alone...

I have the sma issue. Looks like the device is deflect and needs to be changed.

Adding new Deco M5 device fails with device being "Not Found". Settingup this device as own network ends up with red LED light and "Deco_A018" wifi without internet connection. Anything else to do...