-

It appears to be that this bug doesn't occur in Vanilla worlds.

-

Sometimes, when a dungeon generates, its chests can be placed adjacent to each other, merging into a large chest.

If you open this chest, no loot generates. But, if you break one of the chest blocks (which only drops itself in this case, no loot) – then open the leftover small chest, the dungeon loot will generate inside.

How to Reproduce:

- Create a "customized" world in Creative Mode, with "Dungeon Count" maxed out.

- Enter Spectator Mode and give yourself Night Vision (Ex: "/effect <playerName> night_vision 10000 0").

- Look around for a dungeons with a double/large chest in. Briefly go to Creative to open the chest. It should be empty.

- Break one of the chest blocks, which shouldn't drop anything. Then open or break the leftover chest. Dungeon loot should appear as expected.