Advancements fail to generate both on a dedicated server and an integrated server when the world is generated. Manually placing them into /data/advancements or /data/advancements/minecraft (having extracted the files from the client jar) also fails to load them. Placing them into /data/advancements/custom causes the server to load them, but still nothing on the client.

Advancements attached (although they are pulled straight from the client jar)