Minecraft wiki entry for Development_versions, associated text: MC-187350 – Game randomly crashes: IllegalStateException: POI never registered.
MC-187352 – Loading a world created in 1.16-pre1 always ask for confirmation.
MC-187353 – Crash when loading some worlds: IllegalStateException: Lock is no longer valid.
MC-187358 – Worlds generated in 1.16-pre1 do not have their world generation settings saved correctly, causing chunk errors.
MC-187364 – Disabling and enabling dimension datapack disables nether and end.
MC-187406 – Game crashes when joining in disabled dimension.
MC-187408 – Game crashing with nether portals: java.lang.NullPointerException: Ticking player.