Why is my imported material blocky?

For some reason, my material appears blocky in the editor after I rebuild the lighting.

^^^Before a lighting rebuild

^^^ After a lighting rebuild

I already made a uv map and a lightmap of this, but I don’t have any other explanation as to why this is messing up. Maybe I made the map wrong? Help pls

Hi!

Could you show us your lightmap and material uvs?
Thank you!

If you made this in blender (or another modeling programming) make sure you have it set to smooth shading instead of flat shading.