I joined online then in practice wether changed from dry to rain, i entered pits (done full lap on dry tyres then ask for pitcrew, entered pits and changed tyres and some damage) when i return to track i could see 3 yelllow kind of boxes instead of cars, after a while i could see all cars as it should.
Those are temp cars. When someone joins when you are on track, it will load a low poly, low detail car to prevent join lags. Once you exit back to the garage, the cars will load.