If the player opens their model's bag too close to a vehicle or loose item on the ground, then it either gets deleted from the game or sent off flying. I believe this is due to the bag being physically taken off of the player's back in order to examine its contents, which pushes anything in the way out of it. I have had to close my game many times without saving in order to recover my convoy at least three times now, and once to collect items I "borrowed" from a corpse.
The first bug I encountered, however, was that, occasionally, when entering a vehicle it would literally collapse, jammi