"ghost" cars in lobbys (mostly in non-race session)

Quick question on how the "ghosting" of cars works in multiplayer, I get that there is a setting to "ghost" a car not moving on track or driving in reverse for example, but I came accross situation where we are going at race speed already and still some cars are "ghosted", while some other are not. It is quite disorienting to suddenly find a ghost in the session and just before you know it the car that was ahead is not and drama follows immediately.

Are there any particular conditions that can make a car at race pace a ghost ?

 

I’m going to assume this was when joining a practice or qualifying session that’s already running .
In this situation the cars already out on track haven’t synced to you yet as that won’t happen until they return to pit .
It’s best practice to treat all cars as not ghost to avoid unexpected contacts.