Suffocating in wall when jumping & crouching
When in a 2 block high space, you can take damage while crouching and jumping at the same time.
https://www.youtube.com/watch?v=Cg-1usLaJQE
Can confirm that it occurs when the sneak button is set to toggle instead of hold.
I was unable to recreate this in Single player, so it probably has to do with online servers. If anyone can recreate in a server, please comment.