Yeelight 650 (ceiling4) not switching off completly

Hello there,

I got two ceiling light 650 (model ceiling4 in local API) and 8 480s (ceiling1). When switching them off by API, APP or bluetooth remote control (230V power stays connected) all switch off completly exept one of the 650s. At this one, the ambient light is off, but the main light stays on a little bit, just a little dimmer than level 1 of the moonlight.
The firmware on the 650s is 56 as reported by the API/2.0.2_0056 by the APP.
Any ideas how to fix that?

Regards, Edi