So you know how fireworks work in minecraft with elytra? You fly, you use 'em, and you go really fast? There's an issue with that. Most of the time, if you boost directly up into the air(It's most efficient for height), it just kicks you out and says "Invalid move player packet recieved" and boots you out to the multiplayer world select screen. Did i mention this happens on single player? And not only that, but sometimes elytra speed just stops completely.

Edit: Sometimes when i do it, when i log back in, i'm below the bedrock(I test on a superflat) and i get kicked out again.