The bug, and how to reproduce:

• Create a root advancement with "hidden": true
• Make an advancement with the parent as the root advancement you just made.
• /reload
• Grant the child advancement
• Look in the advancements menu, and the advancement you made will be there, even though the root is "hidden": true.
• Also note that the root advancement icon is not there. See attachment.

Also applies to "announce_to_chat" too.