Very weird lightmass diffuse error

I’m working on a level right now in 4.12.5, and lightmass is giving me some crazy results every once in a while, it’s very inconsistent! I’ve no idea what’s going on with it or why these errors are occurring. I’ve added images of my settings etc, if need anymore info, let me know!

115558-lightmass.jpg

I’m using multiple lightmass importance volumes, and they overlap some, could that be the case?

The weirdest thing is, that bright orange color sometimes appear in different location in the level! And I have to build lighting multiple times until I get correct result.