Old villagers can't trade

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The Video:

https://youtu.be/gj4TuwraYNQ

Could you show the NBT of the villagers? (/data get entity @e[type=villager,sort=nearest,limit=1])

Here's the nbt

 1.20.4 Villager has the following entity data: {Brain: {memories: {"minecraft:last_worked_at_poi": {value: 26332L}, "minecraft:job_site": {value: {pos: [I; -58, 72, 31], dimension: "minecraft:overworld"}}}}, HurtByTimestamp: 0, Attributes: [{Base: 48.0d, Modifiers: [{Amount: -0.013233750057890462d, Operation: 1, UUID: [I; -1134045425, -507688179, -1912325114, -1462673189], Name: "Random spawn bonus"}], Name: "minecraft:generic.follow_range"}, {Base: 0.5d, Name: "minecraft:generic.movement_speed"}], FoodLevel: 0b, Invulnerable: 0b, FallFlying: 0b, ForcedAge: 0, Gossips: [{Target: [I; -1666807936, -830519434, -1508254147, 1611017848], Type: "trading", Value: 8}], PortalCooldown: 0, AbsorptionAmount: 0.0f, LastRestock: 26030L, FallDistance: 0.0f, DeathTime: 0s, Xp: 376, LastGossipDecay: 4069L, HandDropChances: [0.085f, 0.085f], PersistenceRequired: 1b, UUID: [I; -1155492370, -1499971357, -1404270544, -39725950], Age: 0, Motion: [0.0d, -0.0784000015258789d, 0.0d], Health: 20.0f, LeftHanded: 0b, Air: 300s, OnGround: 1b, Offers: {Recipes: [{maxUses: 16, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 1, id: "minecraft:emerald"}, buy: {count: 15, id: "minecraft:beetroot"}, xp: 2, priceMultiplier: 0.05f, demand: -32}, {maxUses: 16, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 6, id: "minecraft:bread"}, buy: {count: 1, id: "minecraft:emerald"}, priceMultiplier: 0.05f}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 1, id: "minecraft:emerald"}, buy: {count: 6, id: "minecraft:pumpkin"}, xp: 10, priceMultiplier: 0.05f, demand: -24}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 4, id: "minecraft:pumpkin_pie"}, buy: {count: 1, id: "minecraft:emerald"}, xp: 5, priceMultiplier: 0.05f}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 1, id: "minecraft:emerald"}, buy: {count: 4, id: "minecraft:melon"}, xp: 20, priceMultiplier: 0.05f, demand: -24}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 18, id: "minecraft:cookie"}, buy: {count: 3, id: "minecraft:emerald"}, xp: 10, priceMultiplier: 0.05f}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {components: {"minecraft:suspicious_stew_effects": [{duration: 140, id: "minecraft:weakness"}]}, count: 1, id: "minecraft:suspicious_stew"}, buy: {count: 1, id: "minecraft:emerald"}, xp: 15, priceMultiplier: 0.05f, demand: 12}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {components: {"minecraft:suspicious_stew_effects": [{duration: 100, id: "minecraft:night_vision"}]}, count: 1, id: "minecraft:suspicious_stew"}, buy: {count: 1, id: "minecraft:emerald"}, xp: 15, priceMultiplier: 0.05f, demand: -12}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 3, id: "minecraft:golden_carrot"}, buy: {count: 3, id: "minecraft:emerald"}, xp: 30, priceMultiplier: 0.05f, demand: -12}, {maxUses: 12, buyB: {count: 1, id: "minecraft:air"}, sell: {count: 3, id: "minecraft:glistering_melon_slice"}, buy: {count: 4, id: "minecraft:emerald"}, xp: 30, priceMultiplier: 0.05f, demand: -12}]}, Rotation: [304.91663f, -33.577244f], HandItems: [{}, {}], RestocksToday: 0, ArmorDropChances: [0.085f, 0.085f, 0.085f, 0.085f], CustomName: '"1.20.4 Villager"', Pos: [-56.38214247321418d, 72.0d, 31.480934292015206d], Fire: -1s, ArmorItems: [{}, {}, {}, {}], CanPickUpLoot: 1b, VillagerData: {profession: "minecraft:farmer", level: 5, type: "minecraft:plains"}, HurtTime: 0s, Inventory: []}

Can confirm I'm seeing this in my snapshot world with the experiments turned on too.

I can confirm this for 24w13a.

Offers:
{Recipes:
[{maxUses: 12,
buyB: {count: 1, id: "minecraft:air"},
sell: {count: 2, id: "minecraft:redstone"},
buy: {count: 1, id: "minecraft:emerald"},
priceMultiplier: 0.05f, demand: 2},

So in order to fix the problem you either need to:

a) Delete the world.  Only anything 1.20.4 and below is effected.

b) Wait for Mojang to fix it

c) Code a mod to fix it yourself on every villager you come across.

d) Remove the "BuyB" tag manually, or any other invalid "Offers" NBT data on the villager.

Have fun.

Had this issue happen last night on 1.20.2 setting up a new trading hall.

Moving villagers from villager breeder, to zombification station, to trading hall.  Have some existing Librarians and a Fletcher which were converted and moved in, working fine.

Proceeded to move a few new villagers, converted and assigned to Librarians and Farmers, a single Armorsmith and single Toolsmith. The Farmers, Armorsmith, Toolsmith and Fletcher were all upgraded to Master rank.

Proceed with the same setup for next villager, setup as a Weaponsmith, got to Apprentice rank and accidentally flipped a trap door and they got out. Broke grindstone workstation and proceeded to catch in mine cart to bring back to cell.  When I place the workstation again, the dual item trade bug appeared and I could no longer trade with the Weaponsmith.

I checked every other existing villager (again some already at Master rank) and they all displayed the same window with two spots. Tried placing emeralds in both slots and still can no longer trade with any villagers who have previously been traded with. 

Not sure if the issue was breaking the workstation while it was upgrading from Apprentice to Journeyman, or something else, but was hoping some extra details may help resolve this issue.

I am able to replicate the issue in a creative world following the same steps. Set villager in cell, give workstation, trade, break workstation, can no longer trade due to dual trade spots displaying even for emerald only trades.

Confirmed 24w14a is still effected.

Will attach entire F3+I tags of the same bugged villager's NBT post 1.20.4 ->> 24w14a World Upgrade.

Looks good using the "EmptyItemInVillagerTradeFix" and it works ideally moving forward;
But I also wanted to mention that the "matchesBuyItems() under "TradeOffer" was the main culprit, where the

"!this.secondBuyItem.isPresent()" logic should have been inverted and tested for this.secondBuyItem.get().match(ItemStack.EMPTY) as well, because reading in the
"Optional<TradedItem>this.secondBuyItem" does not check for minecraft:air, it only checks for the presence of data, which lead to this bug since 1.20.4 and below writes minecraft:air to any "Empty" trade slots.
👍

I seem to be having this issue in 1.21.1, what do I do?