Send your fbx to me. I have Blender 2.9, so I’ll check it in there and try importing to Unreal 4.25.3, and 4.24.3. I’ll try doing a mirror in Blender and then import to Unreal too. I’ve seen a problem before with mirroring in Blender and importing to Unreal, in another thread, and it was with a pre-made mesh. I don’t recall the fix that solved the problem, but if I’m capable of finding the thread, I’ll post a link to it.