Two pieces are swapped
On a 3x3 cube you can't swap just two pieces by turning. Pieces always move in a way that would also swap another pair. So "two pieces are swapped" means:
- Two stickers were misread. This is far more common. Swapping two stickers between two pieces looks exactly like swapping the pieces.
- The cube was put back together wrong. Two edges or two corners were swapped by hand.
How to fix it
On the Check step, compare each sticker with your cube. Light reflections and red/orange mix-ups are the usual causes.
If the scan is right, pop the cube apart:
- Turn the top 45°.
- Lever out one edge.
- Swap two pieces back.
Any two edges, or any two corners, restore a cube that can be solved.
Common mistakes
- Swapping stickers instead of pieces. If someone has peeled stickers and moved them, the cube may need re-stickering.