My arms and legs disappeared from my avatar after flying with elytra and fireworks in creative mode. I was also diving into the water from flying because it's so smooth diving into water with the new sprint-swimming.
I used a few fireworks, then it they ran out. But I think the game glitched, I rubber-banded back a little bit, the fireworks went for another second or two, then I entered third person to see that I have no arms or legs.
Possibly has something to do with the new animations for sprint-swimming?
Previously happened to this person: https://www.reddit.com/r/Minecraft/comments/7xk1he/in_the_last_snapshot_be_careful_with_your_legs/
And also this person (@@unknown): https://www.reddit.com/r/Minecraft/comments/7veimo/turtle_shoutout_to_billyk_as_suspected_theres_a/