I’ve scene a few posts about the build lighting process getting stuck across multiple versions of UE4 and run into it fairly frequently myself in 4.9.1.
I have at least one easily reproducible case here:
1.) File → New Level → Empty Level.
2.) Add BSP box of 1000, 1000, 400 to scene and mark it hollow.
3.) Place a couple of point lights inside the hollow box and make both static.
4.) Convert BSP box to static mesh.
5.) Open static mesh and set it’s lightmap coordinate index to 1 and save it.
If I try to build lighting at this point it sticks at 66% and never finishes.
This is an issue that has been re occurring throughout 4.9.
After following your steps, I’m assuming the 1000,1000, 4000 is referring to the scale of the bsp, and building lights my lights built to 100% and finished.
Could you link me your DxDiag and I will see if this issue has been reported with your specs.
I just tried this reproduction that you mentioned and I was able to build.
I believe this to be another issue we have been having with lighting builds. What will happen is the lightmass will run but the build will stick at a certain percentage. We are currently investigating this issue and your thread has been added to the list of users currently experiencing this issue. Hopefully with a large amount of issues from the community this will be resolved very soon.
The ticket number is UE-20782.
I will keep you up to date with this bugs progression.