Static lights black after build

I have this static mesh that represents a cave. It works fine with stationary lights. It also appears ok while in “preview mode” with static lights, like the imave below:

However, after build the lights (using a static light), the light disapears completelly:

The lightmap seems ok to me:

Both light and mesh are configured with static mobility:

I saw a lot of similar issues around the internet, but was not able to find an answer. I have no idea what is going on and how to fix it. Any help will be appreciated.

Well, like always happens after I post something here, I figured out the issue a few minutes later.

The ambient occlusion of my material was bad configured and it became 100% black. I still not sure why it only affects the static lighting, but it also explains why, in other situations, my scenes always became a bit more darker after the light build.

How was the ambient occlusion badly configured in the material?

AO has nothing to do with direct light.

Then why would having a bad configuration of AO in the material cause it to be black? I think it would quite probably overwhelm or cover over the direct light, or perhaps mix with it if it was getting diffused everywhere in the scene. But in a cavern, there’s a different type of light bouncing happening, so it could be something other than the AO was doing it too.

Most likely they had a 0 plugged into their material’s AO channel or a black texture map

This is true for stationary and dynamic lights, but static lights will use the material AO input. I assume the lightmap contains no information about static lights type or orientation so it just treats it all as indirect.