Looking at the scene you have uploaded, it seems as if the model had problem with smoothing. I think the whole object should be smooth - each vertex should have one common normal for all the triangles it belongs to. However, the shading is not smooth, there are some vertices which have different normals for different triangles they belong to, which leads to “hard edges”.
Incorrect smoothing causes artifacts both in static baked lightmap, and in dynamic reflections or simple lighting model (where lightmap isn’t used).
If the model was imported to SketchUp from some other source, then the original normals might have been lost. Is the model still smooth in SketchUp when you enable the View > Edge Style > Profile or does it have some edges? What you could do to remove such edges is increasing the threshold for this object in the Soften Edges tool of SketchUp.
Let us know if it helped.