It's also possible that they knew the comment would somehow touch a nerve, or something, and they didn't want to go there. Maybe not for you, but for somebody else. Or maybe the offshoot was something that the other people did together, didn't want to include any others, but didn't want to talk about in front of somebody not included, and so they thought it better not to respond and to delete your comment when you asked again. It's a long shot. But even if they weren't talking about an event. Like maybe the conversation was about line art, and somebody mentioned stamping. You asked about stamping, and nobody wanted to respond because they're all in a group that does stamping together, they don't want new members, and they didn't know anything to say that wouldn't be talking about it in front of you.