This feels like a common courtesy I don’t see enough, particularly the second point. In a conversation circle, always try to keep your side vision open to people trying to find their way in. It can be awkward to try and find your own way in so giving them a spot tells them they’re included then drop a quick brief on the conversation “We’re talking about pineapples on pizza, good or bad” gives them context to jump in immediately.
I recently was at a party and was kind of shocked at how many people don’t follow what I considered to be the norms of group conversation. When a conversation circle forms, I think it’s polite to acknowledge other people. If someone new joins the circle, at least say hello or acknowledge them with body language. It’s uncomfortable to walk up to a circle and feel iced out because no one even looks at you. I also think it’s rude to monologue or tell everyone your whole life story. It’s appreciated to engage with other people, and give them the opportunity to talk.
I think some of the people were just socially awkward and clumsy, but I also suspect some people are still mentally High School and were ignoring other people on purpose.