Im having this issue with some of my models. I dont know why look like this. It doestn matter if I change the texture it always looks bad.
That might be a normals problem or a lightmap problem I suggest checking both. For the lightmap open the static mesh in the content browser and on the top of the window there should be a UV channel option, change it to 1 and check that those UVs are good. If that’s not the problem then enable the normals view to see if they are flipped.