The Fibaro RGBW Controller is a VERY strange device. I’ve used all the available device handlers for this module, and it’s been very frustrating. The problems I’ve had are, like yours, turning on faded right down, or 20%, turning on and randomly changing colour (so when it’s red my house looks like a brothel), either the On or Off tile not registering in the app, not being able to easily configure the parameters settings within the app, too many to mention.
The solution that is working for me is this device handler…
And to be doubly sure I’ve used a CoRe piston to when turned on go to full brightness, it’s been a week, with three Fibaro’s and no problems.