The bug
Standing inside a block or having a gravity enabled block fall on you triggers the elytra animation and pulls you down into suffocation.
MC-147422
Suffocating in one block at feet
Resolved
Fixed
4
Ayden Hodgins
migrated
Confirmed
Minecraft 19w14a
Minecraft 19w14b
Retrieved
This is also activated by being within a doorway when the door closes. No suffocation damage is taken in this case, but it looks strange visually.