I created a random world, as normal, and then started dying. Turns out I had been spawned literally inside packed ice blocks.
Seed was 1190874297498346625, spawn position is about 8/66/8. Did the same with that as a set seed to confirm that it is reproducible.
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I am able to confirm this behavior. This closely relates to MC-236837. Here are some extra details regarding this problem.
The Bug:
The player can occasionally spawn inside of blocks and begin suffocating when loading into a new world.
Please note that you may need to load a new world with this same seed multiple times as you don't always spawn in the exact same location when loading into a new world.
Steps to Reproduce:
Create a new world with the following seed.
Seed: 1190874297498346625
Observed Behavior:
The player can occasionally spawn inside of blocks and begin suffocating when loading into a new world.
Expected Behavior:
The player would not be able to spawn inside of blocks and begin suffocating when loading into a new world.

Can confirm. Spawned inside of a iceberg. Seed: 3423331061424976455

Dupe of MC-132347