HUE Bulb is switched on and delays dimming, why?

Hi everybody,
I have the problem that my lamp is switched on with low brightness (typically HUE) and then dims up. However, the dimming sometimes only takes place after a 1-2 second delay, which can be clearly seen.
Does anyone else have this problem? Does anyone know what’s going on?
My HA is running on PI with deconz stick.
Thanks for your feedback