Most Ford products are designed so the seat belt latch by the center console moves with the seat. The bottom of the latch rides on the seat rail, and with time sometimes it builds up a little play on the rail. As the seat moves forward or back, the seat belt guide often tilts forward or back, just a bit, on the rail, and gets stuck. So you can move forward or back just a bit, but then it jams and you can hear the motor, but can go no further.

The long term fix is to remove the seat, disassemble the seat belt guide and rail, and usually replace some parts.

But the short term solution is often to simply hold on to the seat belt latch and rock it forward and away from the seat as you try to go forward or back. Or, sometimes it works best to rock it backwards and away from the seat as you try to move forward or back. It all depends on which way it is binding.

There's no guarantee that it won't jam again if you move it all the way back or forward, but once you find the right position to hold the seat latch in while moving the seat, you should be able to re-adjust it where you need it to be.