Datafixer issues
MC-104897End crystals placed on exit portals generated before 1.9 do not respawn the ender dragon
Fixed
MC-122995BlockEntityTag data fix walker is incomplete and incorrect
Normal MC-135413Datafixers.Dynamic can't convert boolean values. always 'false'
Plausible
MC-140565Patrol leaders with banners can drop 2 different types of banners which don't stack
Fixed
MC-150635EntityCatSplitFix does not properly retain newly set Trusting tag during datafixing
Confirmed
MC-153039Console spam: Unsupported key: minecraft: in TaggedChoiceType. Entities from 1.10 crash the server
Awaiting Response
MC-154032Librarians created pre 1.14 don't apply discounts to book trades.
Plausible
MC-155097Scoreboard objectives lost (not updated when converting a world to version with renamed stats)
Confirmed
MC-158853Chests missing after converting and loading old map from 1.7.10
Fixed
MC-167027"Error while deserializing" in console when converting a 1.14 world to 1.15
Normal MC-167363Wolf collar color changes when upgrading pre-1.8 worlds
Confirmed
MC-169769Incomplete registration of entities for Item data conversion
Won't Fix
MC-172027Datafixer for minecraft:recipes/misc/composter advancement is missing
Fixed
MC-172078All villagers with saved memory disappear when upgrading to 20w07a
Fixed
MC-175185No datafixer for item AttributeModifiers UUIDs
Fixed
MC-176011Minecraft 20w13a server spamming chat after update
Fixed
MC-177336'Failed to access level' when opening a world from a CIFS mount on Ubuntu
Fixed
MC-177446"RootVehicle" tag in playerdata entry is not upgraded
Fixed
MC-179866In some spots, it is raining even if it should be snowing
Fixed
MC-181270Trying to open old worlds (in Region format?) without version information in snapshots does not show warning screen
Fixed
MC-181507Worlds that have an unknown version now show the latest version
Duplicate
MC-181511Chunks with redstone are removed
Fixed
MC-181522Chunks that haven't been explored since 1.13 are resetting
Fixed
MC-18251415 Block States per SubChunk Limit during World Upgrade
Fixed
MC-184608"Unknown biome, defaulting to plains" error upon launching the game
Fixed
MC-184740Structures generated in previous versions are not recognised as valid structures, causing mobs not to spawn
Fixed
MC-186087World Seed reset to "0" after upgrade from one snapshot to another
Won't Fix
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