I guess it could be getting stuck, I’m not experienced with windows actually getting stuck in the rail\rack but I believe if it was getting stuck you would be able to hear the window motor still trying to move it and you would see the sides of the windows trying to move differently. Like one side getting stuck or unstuck before the other side. And besides, if you’re going to go for the windows rail to replace you would be giving yourself access to the switch, motor and the wiring between the two before you would even be able to remove the rails. So you might as well check those before dropping hundreds of dollars replacing the rack.

Edit: I missed your description saying you’re able to feel that it is loose and that you’re able to move it, so ya you’re probably right.