I've been in a number of these discords,actually a mod for one of them, and I can say that it's less "sneak-dissing" and more of people just venting what they've already talked about in the threads directly to whoever they were talking about or whatever topic they disliked. They'll even be in the same server as the person they disagreed with and will still vent. They usually talk it out, and it's done -- over with. Let's be honest -- you will not like everyone and not everyone will like you. As noted in the following thread, most people think this way:
Yeah, there is a rot in the forums. We still get people who have already been banned but keep coming back again and again under different accounts. Threads have been shut down because things became too heated. There are also users who purposefully misunderstand things (might even lie) in order to serve up drama both in the forums AND within some of these discords. Won't say who some of these users are, but it gets to the point where they're either banned or ignored until they leave. So yeah -- there is a rot.
But, as far as I know, when it came to these servers, no one had ever said "this person shouldn't make comics because XYZ". They have questioned the content and context of their work, which was also stated in the forums directly to the person.
Now, how to combat it is another thing to talk about. After all, even with banning, we still had people coming back. So I do question that, even if the forum mods talked to them, would they change their behavior?