I was unable to build my light, and after a few hours trying to fix it, and reading about it here and on the answers hub I couldn’t find any solution, them I started to check if my computer was the problem, and here is what I found.
On mac if you go to System Preferences > Security & Privacy > Firewall > Firewall Options
you wanna to allow incoming connections for the “UnrealLightmass”
(after doing this now I can build my light)
Problem was UE4 never asked me to allow it, and when I tried to build the light it would just stay at 0%.
I reinstalled the engine multiple times, and this never came up, and who would guess the unreal lightmass need to connect.
Can anyone tell me why does it need to connect to the web? And are there other things that need to connect? Would be good if the engine gave a warning for this kinda of thing.