Object's materials mixed up on export

I was trying to remove a couple of road signs from a traffic light model from sample city, but upon exporting it as fbx and removing the signs in blender some materials got mixed up, such as the pole having banner’s texture.

I’m not entirely sure what the source of this issue is or how to fix it, should I be using some specific export/import options to prevent this from happening? Is it possible to remove the signs in Unreal without exporting?