Hey,
I'm not sure, if I'm in the right subforum here...
In the 1.5 daily build the Lightmixer randomly turns on/off and is sometimes not reacting to changes while behaving in this strange way. I have a scene were I set all my lights in lightmixer and then the lights go back on/off (maybe back to beautypass, I don't know). Problem is solved by saving the preset and then loading it again or sometimes just by changing the value for one light. And to be clear - the values in Lightmixer are not changing, it's 'just' the render view.
Best