If you try to download worlds from the Retail version of Minecraft while on Minecraft Preview - the Resource packs will move over, But the behaviour packs will not.
steps to reproduce:
Create a world on Minecraft and import a resource and behaviour pack.
Load Minecraft preview and sync retail worlds. Now download the world you created.
Load the world to see if everything worked.
Observed results - the Behaviour pack did not transfer although the resource packs did.
Expected results - both packs should transfer.
Regalo james