I'm able to get the light mixer to function properly and a new scene, but I'm having trouble in a much larger project file. The IPR will almost always restart when I adjust my light mixer lights. I tried soloing a few objects/lights in my scene which made it a slightly more stable.
I should mention that regardless if I'm using the light mixer my IPR will automatically refresh without any user input about 20% of the time. I'm not sure if that is typical behavior or not, I've kind of just dealt with it.