When exporting, goto geometries tab and change smoothing from normals to faces. As for the triangles error I’ve never seen it. Unreal will auto triangulate. You could try ctrl t in blender. That will triangulate it and then export. If it doesn’t work care to share the fbx? I’ll give it a look over
Also side note. In general I also check selected objects when exporting just in case there is any other objects in scene I forgot about when exporting, otherwise blender will export everything in the current layer you are in. If maybe possible there is a plane you deleted in edit mode but the origin is still in memory with one vertex flying around, that may cause the error because there isn’t really anything there for unreal to triangulate. Maybe. Shot in the dark.