Moved to a different railcar would require loading and unloading at a facility. Considering all those are reporting the same thing, then my guess is the rail car had a problem enroute and had to be set out on a siding for repair. This happens from time to time as the railroads have defect detectors along the mainlines to try and detect issues with trains before they create larger issues, such as a derailment. If the car tripped a defect detector, the train crew has to stop the train and visually inspect the railcar. If something is discovered to be wrong that the train crew can not resolve, then the car is setout at the nearest siding for repair and the train continues. Once a maintenance crew repairs the issue with railcar, dispatch will usually schedule it to be picked up by either a local or another through freight train. Considering that it's been a week with no movement on the railcar, this would be my best guess as to what happened.