Underground base becomes void after updating from 26.3 Snapshot 6 to Snapshot 7

Short description:

After updating an existing singleplayer world from Minecraft Java Edition 26.3 Snapshot 6 to 26.3 Snapshot 7, a previously generated underground area containing my base became void.

The world worked normally in 26.3 Snapshot 6 before the update. After opening it in Snapshot 7, the underground base, the surrounding underground terrain, and the bed inside the base were missing. The player fell into the void when the area loaded.

The entire Overworld did not become void. The issue affected the underground area where the base had previously existed.

A separate world spawn point had also been set using /setworldspawn at another underground location in the Overworld, far away from the base. After the bed disappeared and the player died, the player did not respawn near the world spawn point previously set using /setworldspawn. Instead, the player respawned at a different location.

Steps to reproduce:

1. Open and play an existing singleplayer world in Minecraft Java Edition 26.3 Snapshot 6.

2. Have a previously generated underground base containing player-built structures and a bed.

3. Sleep in the bed to set the player's personal respawn point.

4. At another underground location in the Overworld, far away from the base, use /setworldspawn.

5. Save and close the world.

6. Create a backup or copy of the world.

7. Open the world copy in Minecraft Java Edition 26.3 Snapshot 7.

8. Travel to or load the underground base area.

9. Observe that the underground terrain, base, and bed are missing and the area has become void.

10. Die after the bed respawn point has become invalid.

11. Observe that the player does not respawn near the world spawn point previously set using /setworldspawn.

Expected result:

Previously generated underground terrain, player-built structures, the bed, the player's respawn point, and the world spawn point set using /setworldspawn should remain unchanged after updating the world.

Actual result:

The previously generated underground base area became void. The underground terrain, player-built structures, and bed disappeared, and the player fell into the void.

The bed respawn point became invalid. The separate world spawn point previously set using /setworldspawn was also not used after death, and the player respawned at a different location.

Additional information:

• Minecraft Java Edition

• Singleplayer world

• Previous version: 26.3 Snapshot 6

• Affected version: 26.3 Snapshot 7

• Operating system: macOS

• Vanilla client

• No mods installed

• No shaders installed

• Screenshots are not available

• Exact coordinates are not available

• The underground base and the location set using /setworldspawn were far apart

• The issue was observed once and was not retested because of the risk of further world data loss