Summary:
Upgrading a world from 1.20.4 to 1.20.5, inventories of trader llamas are shifted, with items lost which end up in invalid slots. Any item in the carpet slot is also discarded. This does not affect regular llamas, only trader llamas.

Steps to reproduce:
You can go straight to step 5 using this world: 2024-04-24_23-54-57_MC-271109.zip.
You can use the command to summon the trader llama to skip steps 2-4.

/summon trader_llama ~ ~ ~ {Tame:1b,ChestedHorse:1b,Items:[{Slot:2b,id:"minecraft:egg",Count:1b},{Slot:3b,id:"minecraft:fern",Count:1b},{Slot:4b,id:"minecraft:dirt",Count:1b}]}

1. Create a world in 1.20.4.
2. Summon trader llama.
3. Tame the trader llama.
4. Equip the chest on it.
5. Upgrade to 1.20.5.
6. Look at the trader llama's inventory.

Observed results:
Items from the two lower slots disappeared, and from the third they moved to the lowest one.

Expected results:
All items will be saved.

Screenshots:
1.20.4

1.20.5