Having the icon for a public transport segment indicate real-time data but having no vehicle for it on the map is not unusual. The icons indicate that the displayed arrival and departure times are based on real-time predictions. These typically come from a separate data source than the vehicle locations themselves. Depending on the public transport agency, they typically match up, but at other times we might only get one but not the other.
So remember: having the real-time symbol (signal waves) in the public transport icons for buses, trains and trams means that the associated times are real-time predictions and not based on the time table; this does not necessarily mean that the real-time vehicle location will be available. Vice versa, we might have the real-time location without a time prediction and hence no real-time icon.