@valerostudio said:
2 things it could be
1- light portals - I find if you set rect lights to portal mode, it just kills LC
2- Displaced materials? If you have a lot of displacement in your scene, try to disable it in your globals and see if thats the issue.
I got that problem too, but this is helpful to me, I'm newbie for this.
Thank you very much 
Regards
Okane81 