When in elytra mode, if you fly up and then begin falling when you're looking straight up, you'll fall for about a second before the game pops up an "Invalid move player packet recieved" message and send you to the server list

You'll also sometimes receive damage just before you get kicked from the world

How to reproduce
I found two methods to reproduce this bug:
1. fly up using fireworks/trident with riptide in rain, then face straight up and fall
2. be in elytra mode in water, swim to the water surface, then face straight up, you'll begin falling like if you weren't in water