Description:

One thing that I noticed during testing of my datapacks was when waterlogged air didn't seem to function properly. You could swim through the air, but you could not drown unless you really tried to, and there was very noisy splashing.

One thing I found out with the testing below is that when your eye level was between the bottom of a block and 2 pixels up from the bottom of the block, you would finally begin to lose air, and keep losing air as well. The distance between the two pixels matches that of flowing water at the lowest height, as also shown in the testing below. However, if you ever left these 2 pixels, you would no longer be drowning and it is as if you are breathing air normally.

So I believe that this can be fixed by setting the liquid height in air blocks to the maximum height possible, whether there is a liquid actually in it or not.

Meaning of pictures:

Each picture alternates shows the difference between vanilla data with regular air and datapack data that waterlogs air. Not in order, apparently, sorry. The vanilla data uses flowing water, while the datapack data uses waterlogged air, and the 2 are compared. They show that both waterlogged air and the lowest water height match when it comes to when the player begins to drown, leading me to assume that water height in air blocks is locked at the lowest height, causing the odd behavior in waterlogged air.

How to replicate:

1. Use the Datapack below to waterlog air blocks, or make your own, and put it in the datapacks folder, located in your world save data. (.minecraft/saves/namespace/datapacks)
2. Load the world if you haven't already. Use /reload to turn on the datapack if it is not already on.
3. Use a NoAI Shulker and stand on it, since blocks cannot bring you to the desired height. (Command: /summon minecraft:shulker ~ ~ ~ {NoAI:1b} )
4. Adjust the Peek height of the Shulker to adjust your height. (Command (replace # with a number between 0 and 100): /data merge entity @e[type=minecraft:shulker,limit=1,sort=nearest] {Peek:#b}] )

From Peek:43b to Peek:49b, the player begins to drown in both the lowest height of water and in waterlogged air.