We tried to import an FBX file and it shows very strange black lines. Are these normals? Is it going to cause an issue? Also, trying to zoom in into this model makes it disappear. Just can't get close enough to analyze anything.
Those lines indicate a parent-child relationship. It's actually a good thing, because it means the hierarchy of your model will still work in Blender! :)
If you find these lines annoying, open up the properties sidebar of the 3D Viewport by hitting N, open up the Display Panel and disable "Relationship Lines".