Is this bug report related to this issue?
I did a third test, and it was unsuccessful as well: https://the.socialmusic.network/t/third-test-federating-a-new-topic-from-tsmn-to-wd/472
I have noticed that our #general category is followed by @deadsuperhero's account on We Distribute. Shouldn't there a follower by the category actor? Sorry, I don't know how the NodeBB federation works and this might make no sense.
Also, you say that federation with https://socialhub.activitypub.rocks/ (also a Discourse) works. Which We Distribute category is federating with which SocialHub category?