The problem
The newly-added advancement recipe_crafted is triggered(or at least - its supposed to) when a player crafts an item. But when attempting to do it with a any type of furnace(regular/blast/smoker) something strange happens - if you attempt to manually craft the item you won't find anything strange, in fact, everything will work as intended and the advancement will trigger giving the player the specified reward. But when attempting to pick a recipe from the knowledge book inside the furnace - the game will automatically give you the "crafted" item without triggering the advancement.

Why is that a problem

This creates a problem for data pack creators who use this method for creating custom items, as they can't execute a function as a reward for getting this advancement - because its not being triggered.

How to recreate the bug

Add the provided data pack to your world.
Place down a furnace.
Now grab a few stones, coal and a potato.
Now try to smelt the stone - this is a custom recipe which should give you an acacia boat. 
Take the boat out, now you will see what is supposed to happen(without the issue) - a message will pop up in the chat saying "Triggered".
Now smelt another stone, when its done smelting and you can see the boat - don't grab it, instead, open the knowledge book in the furnace and press the "cooked potato" recipe - you will see that the boat is automatically added to your inventory(so you are essentially picking it up) but the advancement isn't being triggered - you won't get the "Triggered" message.
You've successfully recreated the problem.

Hope I managed to help and that it would be fixed in one of the upcoming updates