How to recreate

1. Use an elytra until it breaks
2. Put mending on it
3. Right-click to switch out with chest plate
4. Use experience to repair elytra
5. Right-click to switch chest plate out with elytra

When held in hand, elytra will look broken, but will not be broken. It also will not look broken while in inventory, or on the ground. Only when it is seen in the hand will it look broken. Later, it fixes itself for some players.