It could do! Let me test that scenario and get back to you.
Discourse publishes activities in a topic to all participants in the topic, even if they’re not following the relevant actor (i.e. category or tag). So this is not expected. It could be a problem on Discourse’s end (please check the logs and let me know if you see anything). It could also be a problem on the platform you’re expecting to see the replies on.
Perhaps give me an example?