The bug
I have downloaded Hidden Valley Survival. It's a Minecraft world for 1.10. I have uploaded this world on my 1.14 server, but I get spam into console and the server stops responding.
The map can be downloaded here: https://www.minecraftforum.net/forums/mapping-and-modding-java-edition/maps/1527322-hidden-valley-survival-tons-of-adventure-dungeons
Log snippet
[21:02:12] [Server thread/WARN]: Unsupported key: in TaggedChoiceType[id, MinecartChest -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["Items", List[MuType[V501_3]]] | NilDrop), NilSave)),
SpectralArrow -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
EyeOfEnderSignal -> NilSave,
ItemFrame -> ((Tag["Item", MuType[V501_3]] | NilDrop), NilSave),
MinecartCommandBlock -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Item -> ((Tag["Item", MuType[V501_3]] | NilDrop), NilSave),
EntityHorse -> ((Tag["Items", List[MuType[V501_3]]] | NilDrop), ((Tag["ArmorItem", MuType[V501_3]] | NilDrop), ((Tag["SaddleItem", MuType[V501_3]] | NilDrop), ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave))))),
Fireball -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
EnderDragon -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartTNT -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Villager -> ((Tag["Inventory", List[MuType[V501_3]]] | NilDrop), ((Tag["Offers", ((Tag["Recipes", List[((Tag["buy", MuType[V501_3]] | NilDrop), ((Tag["buyB", MuType[V501_3]] | NilDrop), ((Tag["sell", MuType[V501_3]] | NilDrop), NilSave)))]] | NilDrop), NilSave)] | NilDrop), ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)))),
ThrownPotion -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["Potion", MuType[V501_3]] | NilDrop), NilSave)),
Guardian -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
SnowMan -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
LeashKnot -> NilSave,
Arrow -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
MushroomCow -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
LavaSlime -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Zombie -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartSpawner -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), MuType[V501_4]),
EnderCrystal -> NilSave,
Snowball -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Enderman -> ((Tag["carried", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave))),
CaveSpider -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartHopper -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["Items", List[MuType[V501_3]]] | NilDrop), NilSave)),
XPOrb -> NilSave,
ThrownExpBottle -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
FireworksRocketEntity -> ((Tag["FireworksItem", MuType[V501_3]] | NilDrop), NilSave),
Chicken -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
FallingSand -> ((Tag["Block", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["TileEntityData", MuType[V501_0]] | NilDrop), NilSave)),
Giant -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
VillagerGolem -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
PrimedTnt -> NilSave,
Endermite -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Creeper -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Rabbit -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ThrownEnderpearl -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Silverfish -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ShulkerBullet -> NilSave,
Shulker -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ArmorStand -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Squid -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Skeleton -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
SmallFireball -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
MinecartRideable -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Wolf -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Witch -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
PolarBear -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Ozelot -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ThrownEgg -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Cow -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Slime -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
AreaEffectCloud -> NilSave,
Painting -> NilSave,
Pig -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartFurnace -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Bat -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Blaze -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
WitherBoss -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
PigZombie -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Spider -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Ghast -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Sheep -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
WitherSkull -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Boat -> NilSave]
...[21:02:12] [Server thread/WARN]: Unsupported key: in TaggedChoiceType[id, MinecartChest -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["Items", List[MuType[V501_3]]] | NilDrop), NilSave)),
SpectralArrow -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
EyeOfEnderSignal -> NilSave,
ItemFrame -> ((Tag["Item", MuType[V501_3]] | NilDrop), NilSave),
MinecartCommandBlock -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Item -> ((Tag["Item", MuType[V501_3]] | NilDrop), NilSave),
EntityHorse -> ((Tag["Items", List[MuType[V501_3]]] | NilDrop), ((Tag["ArmorItem", MuType[V501_3]] | NilDrop), ((Tag["SaddleItem", MuType[V501_3]] | NilDrop), ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave))))),
Fireball -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
EnderDragon -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartTNT -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Villager -> ((Tag["Inventory", List[MuType[V501_3]]] | NilDrop), ((Tag["Offers", ((Tag["Recipes", List[((Tag["buy", MuType[V501_3]] | NilDrop), ((Tag["buyB", MuType[V501_3]] | NilDrop), ((Tag["sell", MuType[V501_3]] | NilDrop), NilSave)))]] | NilDrop), NilSave)] | NilDrop), ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)))),
ThrownPotion -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["Potion", MuType[V501_3]] | NilDrop), NilSave)),
Guardian -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
SnowMan -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
LeashKnot -> NilSave,
Arrow -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
MushroomCow -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
LavaSlime -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Zombie -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartSpawner -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), MuType[V501_4]),
EnderCrystal -> NilSave,
Snowball -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Enderman -> ((Tag["carried", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave))),
CaveSpider -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartHopper -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["Items", List[MuType[V501_3]]] | NilDrop), NilSave)),
XPOrb -> NilSave,
ThrownExpBottle -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
FireworksRocketEntity -> ((Tag["FireworksItem", MuType[V501_3]] | NilDrop), NilSave),
Chicken -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
FallingSand -> ((Tag["Block", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), ((Tag["TileEntityData", MuType[V501_0]] | NilDrop), NilSave)),
Giant -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
VillagerGolem -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
PrimedTnt -> NilSave,
Endermite -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Creeper -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Rabbit -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ThrownEnderpearl -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Silverfish -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ShulkerBullet -> NilSave,
Shulker -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ArmorStand -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Squid -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Skeleton -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
SmallFireball -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
MinecartRideable -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Wolf -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Witch -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
PolarBear -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Ozelot -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
ThrownEgg -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Cow -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Slime -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
AreaEffectCloud -> NilSave,
Painting -> NilSave,
Pig -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
MinecartFurnace -> ((Tag["DisplayTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Bat -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Blaze -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
WitherBoss -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
PigZombie -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Spider -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Ghast -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
Sheep -> ((Tag["ArmorItems", List[MuType[V501_3]]] | NilDrop), ((Tag["HandItems", List[MuType[V501_3]]] | NilDrop), NilSave)),
WitherSkull -> ((Tag["inTile", NamedType["block_name", (Int | NamespacedString)]] | NilDrop), NilSave),
Boat -> NilSave]
...
Is this still an issue in 21w20a or later?