Similar situation here with passenger side seat-belt. Mine will stop in the middle of it's travel though, for instance
When exiting the vehicle, open the passenger door and the seat-belt will begin to move towards it's fully front position along the rail, to make exiting the vehicle easier. Occasionally it will just stop before it gets there at a random position and stay there until the door is closed, at which point it will go back to it's rear position.
It also occasionally does what you describe, too. Not functioning at all. Opening the door and it remains fully to the rear position, making the person entering the vehicle have to sit down and then pull the belt around to the front of their chest. It's annoying.
That being said, the seat belts are *supposed* to work like this;
Ignition on, door closed: Seat-belt fully towards rear (to restrain)
Ignition on, door open: Seat-belt fully towards front (to be out of the way)
Ignition off, door closed; Seat-belt fully towards rear (to restrain) (After ignition has been "ON" and seat belts were previously already at a restrained position)
Ignition off, door open; Seat-belt fully towards front (to be out of the way)
Closing the door with the Seat-belt in it's fully forward position with the ignition off, it will remain there until the ignition is turned to 'on'
The only time the seat-belt will stop when it is in between either the fully forward or fully rear positions is when it is in the process of moving towards one of those positions and you cut power to it (by turning the ignition to 'OFF' or disconnecting the battery; however even with the ignition in it's off position, no matter where along the rail the seat-belt stopped, when you open the door it should still go to the fully front position)
So in my mind the OP's problem may very well be a sticky door switch. Two ways to figure that out;
Does your dome light react to the door being opened/closed?
Does the in-dash indicator for the corresponding door light up when it's opened/closed?
and in my mind for my problem when the seat-belt doesn't move at all;
same as above
and/or possibly related to
reasons why my seat-belt gets 'stuck' at random points and remains there
??? No clue really. Could be perhaps a foreign object in the way on the track
could be a break in power to the actuator...haven't tested it.
Any other ideas?