When Exporting in Blender FBX options> Geometry, set Smoothing to FACES and export again and see if that helps. I have seen something similar when exporting also because making in Blender using Quads, but when it is exported it is converted to Tri s. Depending on how your UVs are laid out, it could also be the lightmap UV. Maybe try increasing the light resolution in Unreal to see if it’s the Lightmap.
other suggestion: Add a triangulate modifier in Blender, then try exporting with Smoothing as Faces. (Unreal should make the lightmap automatically for you if you haven’t changed the setting under import settings for Unreal.)
Good Luck!