@eeeee it is likely due to audience.
So, what happens on your end is you make a topic and mention the Lemmy community.
When NodeBB federates that post out, the Lemmy community is included in the mentions, but it also specifies your category 18, World Chat, in audience.
If Lemmy sees that, and it doesn't know about that community already, it will drop the activity immediately. If it does, then it will likely slot the post into the "World Chat on isurg.com" community on that Lemmy instance.
Lemmy removed audience checking, so this might be a non-issue. Once that Lemmy instance updates to the latest version, it'll hopefully post to the correct community.
That's a tricky one, though, because which community should it post to?
"Medicine" on mander.xyz, or
"World Chat" on isurg.com?
