This led me to @neatchee, who is the instance owner. You might try following them, but I agree, that's an odd bug.
Oddly enough, even users I have already followed do not have their content federated to these magazines at times, even though I have checked their history and seen them use the tags I've assigned to the magazines. I could simply be doing something wrong, but I'm not sure what it is.
Yeah, posting to Kbin from Mastodon instances is a challenge. Kbin filters and tries to assign incoming hashtags to existing magazine hashtags.
If a post contains a hashtag that is taken by another magazine, that magazine usually gets the content instead of yours. Your magazine's hashtag has to appear first in the text. Your Japanese forum is probably catching all of the #japanese posts before they get to LearnJapanese.
Second, it's random which of your magazine hashtags will pull content and from who. The order of the hashtags doesn't appear to affect this.
The only way to ensure a post gets from Mastdon to Kbin or Lemmy is to put @yourmagazine@kbin.social in the post tag. This will make sure it shows up on Lemmy, and will get your post to the Kbin Microblog of the magazine 90% of the time. If you want to be extra sure, do it like this:
@yourmagazinename@kbin.social #yourmagazinename (then any following hashtags)
daredevil