Using the same seed and going to the same chest in the same structure will yield different loot each time you load a new world with that same seed.
2 ways to reproduce:
Create a world with a Bonus Chest
Check chest, note loot
Exit world, recreate world
Check chest in this new but identical world
Loot is different
Create a world
/locate Mineshaft
Look for a minecart with chest
Note coordinates
Check loot, note loot
Exit world -> Recreate world
TP to coords of minecart with chest
Check loot, there's different loot
EDIT: It turns out that the loot chests' loot table seed is being set, but it's not being set depending on the world seed. I found this out with /data get block <coords>.
EDIT 2: I know that this is not WAI because if you read this, you will see that the data structure block sets the loot table seed dependent on the world seed. This was also the behavior of chests in structures prior to the introduction of loot tables, and I see no reason why they would set the loot table seed in new structures, but not old ones that don't use structure blocks.
Linked issues
Comments 7
@qwerty23495, I left this issue alone for a while because I got busy with real life stuff and assumed that this would remain obscure. Thankfully, I was wrong.
On another note, several unrelated issues are linked to this one as duplicates. I have a feeling that someone doesn't quite understand this bug. It doesn't make chests in a structure have the same loot, but rather makes a chest in a structure not have the same loot through multiple creations of the same world with the same seed.
@redstonehelper and @Neko, please remove these so called "duplicates". They're not duplicates of this bug.
Fixed. Sorry about that.
This seems to be fixed with mineshaft minecart chests, but not with bonus chests.
Fixed with Desert Temples too. Just use the seed "CROWTIN", use /locate Desert_Pyramid without moving from spawn, and inspect the chest contents. There should be an enchanted book with Aqua Affinity in one of the chests. Then recreate the world and repeat.
Resolving as CR since we don't know at what point this got fixed.
Can confirm in 1.13-pre5.
Please keep the ticket updated.