Easy to recreate... if enough lag exists like my switch is having... save the game while in the top layer of an ocean biome standing on top of a chest/double chest/ender chest... then upon loading my game lags so badly that even with highest respiration enchantment ALL air bubbles are gone and i start to drown...
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GoldenHelmet
migrated
Resolving as a duplicate of MCPE-84023. The issue here is that you fall through the chest when you load the world.