Thanks for posting pics.
Which version of Unreal are you currently using? I’ve checked the uploaded version and all is well there.
These aren’t artifacts, but simply how the 3D app bakes ‘non-UV’ space. Basically, it looks like your UVs somehow got messed up. Any chance you exported/re-imported the mesh? It almost looks like it may be using the lightmap UVs as the texture UVs.