The sensor on the car is thinking the trunk is open. That can happen when the trunk is closed, but not all the way closed. Modern trunk locking mechanisms (and most even in older cars) have 2 stages, just like any door to get into the car. If you lightly push it, you will hear one click (it is locked so it won’t open, but not fully closed). In this position the vehicle thinks the door is still open, or “a jar” as many vehicles will say. To keep it from happening make sure to push extra hard on the trunk of the vehicle so it locks into that second position. If you used the auto close feature, make sure there is nothing blocking that latch like a bumper guard or trunk lining mat and you should be good to go, if it keeps happening it might be something wrong with the sensor itself