Weird Volumetric Lighting

I’m not sure if this belongs in the rendering section, but before I build my level in Production, my volumetric light shafts look great:

But after building, the lighting and fog mess up, and I have no clue how to fix it:

As you can see, light shafts are coming through the “solid” ceiling, the shafts coming through the windows are no longer defined. I want the lighting to look like the pre-build, but in production quality, if that makes sense.

Any ideas on how to fix this?