Navigation building completed but shadow disappeared

Hello everyone,

I have an interior scene and it looks like this in preview:
81fa3c684a14902ca2f2ad463cb8a66a5a9fa58a.png

After I built the light, the shadow disappeared. It looks like this:

I’ve been looking into other similar questions at UE4 forum and tried to enhance the lightmap resolution to 4096, but the shadow still disappeared after building.
Can anyone please tell me why this happened?
Thanks in advance!!

Most likely your UVs for the lightmap channel aren’t properly done or set.