Bit of a thought experiment here as to how to handle these duplicate accounts.
(tl;dr two federated accounts with different IDs report the same webfinger handle, what do?)
Let's say @ruario@social.vivaldi.net posts an English article under his account (and then is federated), and posts a translated Japanese one that is also federated, but under the Japanese ID.
What should NodeBB do when encountering the latter? Currently, it will try to assert the actor, fail the webfinger backreference check, and probably drop the post. Not so good.
One could adjust the actor to the former (canonical ID), but that's not technically right either.
That also opens up potential account impersonation possibilities, so that is something that would need addressing as well.