When Vadim and Irina arrive, Vadim gets out of the vehicle and is greeted by Slava. He turns back to the vehicle and assists Irina out. Then, from the snow nearby, he picks up a backpack that was not there before.
Vadim and Irina arrive in a vehicle that is not seen again. There is no evidence of anyone else driving it, but it seems to have been driven away or else just disappeared. It raises the question of how were they planning to leave after their sojourn in the cave, if the vehicle has gone.
There is no explanation for how the older detective could've discovered the entrance to Romash's hideaway in the ceiling above a hallway. The entrance is an ordinary ceiling panel that looks fixed in place, in an obscure corner of a large building, with no sign that a secret crawlspace is hidden there.
If Vadim and Irina were to spend a day or two in the cave, then they would need more luggage than the less-than-full backpack that Vadim carries into the weather station. Irina does not bring any luggage out of the vehicle nor does anyone else collect any for the couple.