Answer
Once any Lobby page is published, it's automatically assigned a system-generated Presentation Object — and viewing/opening that lobby (even by the same user who created it) is gated by that Presentation Object being granted through a permission set, exactly the same as accessing any other standard page. There's no automatic 'you created it, so you can view it' exception; the creator needs that specific generated Presentation Object granted to their own permission set (typically done by an Admin after the fact) before they can actually open their own newly-created lobby.