Hey,
I guess I found problem for a lot of Mac users having stuck 0% issue and OS X build in Firewall active.
Following this post ([BUG] Building Lighting in OS X Editor stays at 0% indefinitely when Lightmass is blocked by firewall - Rendering - Epic Developer Community Forums), I tried to allow incoming connections for UnrealLightmass and Unreal Editor in my Firewall on my Mac and building Lightning will never stuck at 0% again.
Lightning building communicates with Editor using network communication techniques.
Try to allow incoming connections for Unreal apps shown in image.
Cheers
