This occured some time ago. I was flying my elytra with a ton of items to test it out but when i crashed and died i teleported back and i found not even half of my items. I even looked in the ocean!
Coordinates: X: 27.404 Y: 74.12213 Z: 313.556
Biome: Mesa/ Deep Ocean
Amount of Items: full inventory and hotbar
Seed: ????