At the start of a new game, after you have placed your banner, an event will occur within 30 seconds. I suppose it’s a bonus event since it’s very predictable. Anyway, this event will not trigger if you pause the game by clicking on the “Pause” icon. It will trigger if you pause the game by pressing the escape key to open the main menu.
I haven’t tested to see if this is something that will only happen with this initial event or if it can occur with other events, but it seems like bad form to have popups happen while you are in the main menu.