Xperia Z5
The player's body goes inside the blocks after diving into the water after flying with the elytra dealing suffocation damage in survival and suffocation effect in creative.
How to produce:
Fill a two blocks deep 2×2 area with water.
Make a two blocks high 2×2 platform of any block.
Wear the elytra wings.
Jump from a high place then fly with the elytra then go straight into the water (from air to water without stopping the elytra glading).
Leave the water and stand under the 2×2 platform that you made earlier.
Start jumping and you should notice the suffocation effect and if you switch to survival you'll get damage.
Update by @unknown:
Video demonstration: https://youtu.be/I2Oq8aWxwzU
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Please add clearer steps to reproduce this issue.
Could it be a duplicate of MCPE-15969?

Weirdly..it has stopped to happen when I just tried it again. And no it's not the same issue as MCPE-15969 but kinda similar. How it has produced earlier:
By placing a block above the player (count three blocks upwards then place it)
Then jumping up or flying upwards while you're under that block.
It shows the "suffocation" effect as shown in the picture.
It's possible to walk into solid blocks sometimes after flying with Elytra equipped.
Steps to Reproduce:
From a height, fly down with elytra into a body of water
Walk into a 1 high gap
Notice your head can clip into a solid block
If you do this in survival you will take suffocation damage

Another was to get the same issue: https://youtu.be/pc-eeYcfkD0

This seems to be fixed in 1.0.5. I'm not sure which build fixed it.

This bug hasn’t been fixed as of 1.14.60.
[media]It also works on IOS devices.

This bug is still not fixed, and we’re in 1.17.10

Excellent observation. I used an Elytra for the first time yesterday. Experienced this. It's in Switch. 1.17.whatever is current (too lazy to open it up). Why is this marked as resolved?

This bug is around for 4 years and still not patched! Wow Microsoft that is truly ridiculous