[Dynamic Worlds] Player instantly falls to their death when loading into a dynamic world (random seed)

Partner Rank: Medium

Verification Builds: 1.21.30 / 27834210 UWP Win 11

Regression Builds: Unknown

Summary: Player instantly falls to their death when loading into a dynamic world (random seed).

Affects currently Live Content: Yes (likely other Dynamic Worlds, and content that we are about to submit)

Impact: Players often fall to their death when spawning into a world, depending on the random seed, leading to frustration and an unfair gameplay experience.

Repro Steps:

1. Install the provided .mctemplate.
2. Create a new world from the template, ensuring that the 'Advanced' tab shows a random seed each time you create a world.
3. Load into the world.

Observed Results:
When the world loads, the player falls to their death immediately. They will be stuck in a death loop, as the player will keep spawning mid-air when they respawn. In 7 out of 10 attempts, players spawn in mid-air and fall to their death. This issue seems to occur based on the topography of the randomly generated seed. Falling to death is common when the initial spawn is too high in the air with no water to cushion the fall. The severity varies depending on the starting terrain — players might land above water, on the ground near spawn, or on tall cliffs. 

Example:

• When the original world seed generated a spawn on a tall mountain, and the random seed created terrain with no safe landing, players would fall from the mountain's height to the ground, dying instantly.

Expected Results:
The player's spawn position should be appropriately reset when a random seed is applied. This means SpawnX, SpawnY, and SpawnZ in the level.dat should clear or reset to avoid unsafe spawn points, similar to how vanilla world generation handles random seeds. The player’s spawn should always be in a safe area regardless of the topography in the generated world.

Screenshots/Videos: Yes, screen recording: (https://capture.dropbox.com/Si8PrlW6Za3eUs13)

Notes:

• Compass documentation suggests deleting the db folder and setting allow_random_seed to true, but does not mention deleting or modifying level.dat in any way, leading us to believe this is a client bug.
• The behavior seems dependent on the original template's terrain and how it interacts with the newly generated random seed.
• The .mctemplate file was sent to Greg via DM on 2024-09-23 to attach to ADO.
• Link to Compass Documentation: Dynamic World Random Seed Guidelines