Encountered initially on February 18th of my 1.15.2 singleplayer, this minor issue occured when I entered a boat that was on land whilst wearing an elytra. I managed to fly and land on top of th boat with the elytra; this unexpectedly suspended me in a crawling-like position, until I either crawl off the boat or right-click it. At that point, I immediately begin to suffocate while I was riding.

The death message after leaving my player to suffocate says:

"[player's name] suffocated in a wall"

What I expected was my player to ride the boat normally, resolving its flight mode state and not suffocate in an invisible wall.

Steps to Reproduce:
1. Grab yourself an elytra and equip it. Place a boat (any variant) on land - not in water.

2. Proceed to enter flight mode and land directly on top of the boat. Ensure that your player remains in flight mode (in a crawling position) while sitting on top of the boat.

3. Right-click the boat to ride. Suffocation begins. (Take note that unequipping the elytra does not stop the suffocation). The suffocation ceases when exiting out of the boat.

Author's note: I've done some research into any bugs related to my finding (especially those to the most recent Java versions), but have not found anything so far. If there indeed is a report regarding this issue already, my apologies! (Also my first bug report :3)

Thanks for your time!