Occurs 100% of the time. Park vehicle and leave the area, or log out. Come back later and vehicle appears normal. Once trying to accelerate the vehicle vibrates aggressively and doesn't move position. Appears slightly lower in ground. Speed shows increase, position remains the same. Reverse and forward appear to slightly move vehicle but soon returns to original position.

Shooting arrows at vehicle sometimes helps to jar it lose, it has worked once for me. Logging out and logging back in does not work, removing tires does not work.

EDIT: The only thing that works is ANOTHER PLAYER climbing into the vehicle for just a second. If he then gets out and original player gets into vehicle, he can drive it away just fine. The other player getting into the vehicle unlocks the car.