Superpings are a chatroom feature only available to diamond moderators, where they can reach a user irrespective of past interaction.
Compare that to a normal ping, where you can @name someone in comments or in a chatroom only if they have been active on a post or in that chatroom.
Superpings have a specific format: @@<chat-id> or @@<site-userid&...
We couldn't decide how best to suppress an attack of the clones... it was a choice between Rick Deckard, and the phantom menace (which undermined an entire franchise).
In the end, due to moral and ethical concerns, we concluded that our successful experiment into cloning had to come to an end, so we are no longer involved in creating clone armies.
Using '@ThePersonsNameYouWantToChatWith' in chat doesn't seem to give them a notification; how can one notify them that you are said something in chat to them?
You can't, unless the person's been recently active in the room you're currently in. Only moderators can use a "super-ping" feature to invite people to chat, even if they haven't visited it before.
Because the user doesn't have a chat account yet.
I just tried searching their username in the list of all chat users and got nothing:
Only users who already have chat accounts can be superpinged just by using @@<username>. For a user who has a site account but not yet an account on Chat.SE, you need to superping them using the <userID>@<...
This will need the attention of Stack Exchange in order to resolve as it is unexpected behaviour with super pinging when notifying users in the instance that other users who active use chat have the same name.
Names on Stack Exchange chat are neither unique or case sensitive. In this instance, there were multiple people named "sven" ...
This issue seems to relate to users who haven't been using chat recently, and therefore whose chat account didn't know about their participation on a particular site. Chat now brutally and relentlessly forces a refresh to their chat data when a moderator uses the @@ trick.
Aka, try again, it should now work.