Why can't I see the people in one of my chat rooms?

in one of the chat rooms that I am a member, I can not see whos present or who have seen the conversation but in another chat room, I can see who has

in one of the chat rooms that I am a member, I can not see who's present or who have seen the conversation but in another chat room, I can see who has seen the conversation even though they don't make a comment. Is there something that can be done so I'd be able to see the other members who have seen the message?

or:in one of the chat rooms that I am a member, I can not see who's present or who have seen the conversation but in another chat room, I can see who has seen the conversation even though they don't make a comment. Is there something that can be done so I'd be able to see the other members who have seen the message?

Tags:conversation,