Thanks for those.
I've figured out it's the 'Snowstorm' addon that's causing the problem. However, I still don't know why unless it was made badly.
Nothing in the Description. This is from the mission.sqm:
class Item397
{
position[]={5845.884277,54.044998,3532.109131};
id=418;
side="EMPTY";
vehicle="MVRSnowstormHeavy";
skill=0.600000;
markers[]={};
};