I've tested with an RHS M4A1 Block II with RHS Mk318 Mod 0 ammo loaded and when shooting at the described areas, there's a random chance to kill the vehicle occupants on first shot.
In the vehicles listed above (only tried those but assume it extends to the whole families), the areas where edges of the armored window glass meet the main armored tub are randomly vulnerable to bullets. Window edges of certain armored US vehicles randomly let through bullets Did you used any other mod when the error occurred?:
